psi2ir: fix nullability assertion generation for platform types

Incorporate PR from Steven Schäfer into IrType-based implicit cast
insertion (commit 17b925636e8717e7648c5d7b792c6ab4d18f776d).

NB this still uses originalKotlinType to determine if the type was
nullability flexible. It is somewhat error-prone and something we want
to get rid of. However, it boils down to some design questions related
to implicit null checks in Kotlin - e.g., it might be Ok to just treat
nullability flexible type `T!` as `T?` in IR, generate null checks for
all usages of type `T?` where a non-null type is expected, and later
eliminate the null checks that are redundant according to the (quite
conservative) criterion in the redundant null check elimination.

compiler/testData/ir/irText/expressions/coercionToUnit.txt

@@ -36,7 +36,8 @@ FILE fqName:<root> fileName:/coercionToUnit.kt
             BRANCH
               if: CONST Boolean type=kotlin.Boolean value=true
               then: CALL 'public open fun println (x: kotlin.String?): kotlin.Unit declared in java.io.PrintStream' type=kotlin.Unit origin=null
-                $this: GET_VAR 'val tmp0_safe_receiver: java.io.PrintStream? [val] declared in <root>.test3' type=java.io.PrintStream? origin=null
+                $this: TYPE_OP type=java.io.PrintStream origin=IMPLICIT_NOTNULL typeOperand=java.io.PrintStream
+                  GET_VAR 'val tmp0_safe_receiver: java.io.PrintStream? [val] declared in <root>.test3' type=java.io.PrintStream? origin=null
                 x: CONST String type=kotlin.String value="Hello,"
       TYPE_OP type=kotlin.Unit origin=IMPLICIT_COERCION_TO_UNIT typeOperand=kotlin.Unit
         BLOCK type=kotlin.Unit? origin=SAFE_CALL
@@ -51,5 +52,6 @@ FILE fqName:<root> fileName:/coercionToUnit.kt
             BRANCH
               if: CONST Boolean type=kotlin.Boolean value=true
               then: CALL 'public open fun println (x: kotlin.String?): kotlin.Unit declared in java.io.PrintStream' type=kotlin.Unit origin=null
-                $this: GET_VAR 'val tmp1_safe_receiver: java.io.PrintStream? [val] declared in <root>.test3' type=java.io.PrintStream? origin=null
+                $this: TYPE_OP type=java.io.PrintStream origin=IMPLICIT_NOTNULL typeOperand=java.io.PrintStream
+                  GET_VAR 'val tmp1_safe_receiver: java.io.PrintStream? [val] declared in <root>.test3' type=java.io.PrintStream? origin=null
                 x: CONST String type=kotlin.String value="world!"

compiler/testData/ir/irText/expressions/implicitCastOnPlatformType.txt

@@ -2,5 +2,6 @@ FILE fqName:<root> fileName:/implicitCastOnPlatformType.kt
   FUN name:test visibility:public modality:FINAL <> () returnType:kotlin.String 
     BLOCK_BODY
       RETURN type=kotlin.Nothing from='public final fun test (): kotlin.String declared in <root>'
-        CALL 'public open fun getProperty (key: kotlin.String?): kotlin.String? declared in java.lang.System' type=kotlin.String? origin=null
-          key: CONST String type=kotlin.String value="test"
+        TYPE_OP type=kotlin.String origin=IMPLICIT_NOTNULL typeOperand=kotlin.String
+          CALL 'public open fun getProperty (key: kotlin.String?): kotlin.String? declared in java.lang.System' type=kotlin.String? origin=null
+            key: CONST String type=kotlin.String value="test"

compiler/testData/ir/irText/expressions/jvmStaticFieldReference.txt

@@ -2,14 +2,16 @@ FILE fqName:<root> fileName:/jvmStaticFieldReference.kt
   FUN name:testFun visibility:public modality:FINAL <> () returnType:kotlin.Unit 
     BLOCK_BODY
       CALL 'public open fun println (x: kotlin.String?): kotlin.Unit declared in java.io.PrintStream' type=kotlin.Unit origin=null
-        $this: GET_FIELD 'FIELD IR_EXTERNAL_JAVA_DECLARATION_STUB name:out type:java.io.PrintStream? visibility:public [final,static] ' type=java.io.PrintStream? origin=GET_PROPERTY
+        $this: TYPE_OP type=java.io.PrintStream origin=IMPLICIT_NOTNULL typeOperand=java.io.PrintStream
+          GET_FIELD 'FIELD IR_EXTERNAL_JAVA_DECLARATION_STUB name:out type:java.io.PrintStream? visibility:public [final,static] ' type=java.io.PrintStream? origin=GET_PROPERTY
         x: CONST String type=kotlin.String value="testFun"
   PROPERTY name:testProp visibility:public modality:FINAL [var] 
     FUN name:<get-testProp> visibility:public modality:FINAL <> () returnType:kotlin.Any 
       correspondingProperty: PROPERTY name:testProp visibility:public modality:FINAL [var] 
       BLOCK_BODY
         CALL 'public open fun println (x: kotlin.String?): kotlin.Unit declared in java.io.PrintStream' type=kotlin.Unit origin=null
-          $this: GET_FIELD 'FIELD IR_EXTERNAL_JAVA_DECLARATION_STUB name:out type:java.io.PrintStream? visibility:public [final,static] ' type=java.io.PrintStream? origin=GET_PROPERTY
+          $this: TYPE_OP type=java.io.PrintStream origin=IMPLICIT_NOTNULL typeOperand=java.io.PrintStream
+            GET_FIELD 'FIELD IR_EXTERNAL_JAVA_DECLARATION_STUB name:out type:java.io.PrintStream? visibility:public [final,static] ' type=java.io.PrintStream? origin=GET_PROPERTY
           x: CONST String type=kotlin.String value="testProp/get"
         RETURN type=kotlin.Nothing from='public final fun <get-testProp> (): kotlin.Any declared in <root>'
           CONST Int type=kotlin.Int value=42
@@ -18,7 +20,8 @@ FILE fqName:<root> fileName:/jvmStaticFieldReference.kt
       VALUE_PARAMETER name:value index:0 type:kotlin.Any 
       BLOCK_BODY
         CALL 'public open fun println (x: kotlin.String?): kotlin.Unit declared in java.io.PrintStream' type=kotlin.Unit origin=null
-          $this: GET_FIELD 'FIELD IR_EXTERNAL_JAVA_DECLARATION_STUB name:out type:java.io.PrintStream? visibility:public [final,static] ' type=java.io.PrintStream? origin=GET_PROPERTY
+          $this: TYPE_OP type=java.io.PrintStream origin=IMPLICIT_NOTNULL typeOperand=java.io.PrintStream
+            GET_FIELD 'FIELD IR_EXTERNAL_JAVA_DECLARATION_STUB name:out type:java.io.PrintStream? visibility:public [final,static] ' type=java.io.PrintStream? origin=GET_PROPERTY
           x: CONST String type=kotlin.String value="testProp/set"
   CLASS CLASS name:TestClass modality:FINAL visibility:public superTypes:[kotlin.Any]
     $this: VALUE_PARAMETER INSTANCE_RECEIVER name:<this> type:<root>.TestClass 
@@ -34,7 +37,8 @@ FILE fqName:<root> fileName:/jvmStaticFieldReference.kt
               if: CONST Boolean type=kotlin.Boolean value=true
               then: BLOCK type=kotlin.Int origin=null
                 CALL 'public open fun println (x: kotlin.String?): kotlin.Unit declared in java.io.PrintStream' type=kotlin.Unit origin=null
-                  $this: GET_FIELD 'FIELD IR_EXTERNAL_JAVA_DECLARATION_STUB name:out type:java.io.PrintStream? visibility:public [final,static] ' type=java.io.PrintStream? origin=GET_PROPERTY
+                  $this: TYPE_OP type=java.io.PrintStream origin=IMPLICIT_NOTNULL typeOperand=java.io.PrintStream
+                    GET_FIELD 'FIELD IR_EXTERNAL_JAVA_DECLARATION_STUB name:out type:java.io.PrintStream? visibility:public [final,static] ' type=java.io.PrintStream? origin=GET_PROPERTY
                   x: CONST String type=kotlin.String value="TestClass/test"
                 CONST Int type=kotlin.Int value=42
       FUN DEFAULT_PROPERTY_ACCESSOR name:<get-test> visibility:public modality:FINAL <> ($this:<root>.TestClass) returnType:kotlin.Int 
@@ -47,7 +51,8 @@ FILE fqName:<root> fileName:/jvmStaticFieldReference.kt
     ANONYMOUS_INITIALIZER isStatic=false
       BLOCK_BODY
         CALL 'public open fun println (x: kotlin.String?): kotlin.Unit declared in java.io.PrintStream' type=kotlin.Unit origin=null
-          $this: GET_FIELD 'FIELD IR_EXTERNAL_JAVA_DECLARATION_STUB name:out type:java.io.PrintStream? visibility:public [final,static] ' type=java.io.PrintStream? origin=GET_PROPERTY
+          $this: TYPE_OP type=java.io.PrintStream origin=IMPLICIT_NOTNULL typeOperand=java.io.PrintStream
+            GET_FIELD 'FIELD IR_EXTERNAL_JAVA_DECLARATION_STUB name:out type:java.io.PrintStream? visibility:public [final,static] ' type=java.io.PrintStream? origin=GET_PROPERTY
           x: CONST String type=kotlin.String value="TestClass/init"
     FUN FAKE_OVERRIDE name:equals visibility:public modality:OPEN <> ($this:kotlin.Any, other:kotlin.Any?) returnType:kotlin.Boolean 
       overridden:

compiler/testData/ir/irText/expressions/sam/samConversionsWithSmartCasts.txt

@@ -106,9 +106,10 @@ FILE fqName:<root> fileName:/samConversionsWithSmartCasts.kt
       CALL 'public open fun run1 (r: java.lang.Runnable?): kotlin.Unit declared in <root>.J' type=kotlin.Unit origin=null
         $this: CONSTRUCTOR_CALL 'public constructor <init> () [primary] declared in <root>.J' type=<root>.J origin=null
         r: TYPE_OP type=java.lang.Runnable? origin=SAM_CONVERSION typeOperand=java.lang.Runnable?
-          CALL 'public open fun id <T> (x: T of <root>.J.id?): T of <root>.J.id? declared in <root>.J' type=kotlin.Function0<kotlin.Unit>? origin=null
-            <T>: kotlin.Function0<kotlin.Unit>?
-            x: GET_VAR 'a: kotlin.Function0<kotlin.Unit> declared in <root>.test8' type=kotlin.Function0<kotlin.Unit> origin=null
+          TYPE_OP type=kotlin.Function0<kotlin.Unit> origin=IMPLICIT_NOTNULL typeOperand=kotlin.Function0<kotlin.Unit>
+            CALL 'public open fun id <T> (x: T of <root>.J.id?): T of <root>.J.id? declared in <root>.J' type=kotlin.Function0<kotlin.Unit>? origin=null
+              <T>: kotlin.Function0<kotlin.Unit>?
+              x: GET_VAR 'a: kotlin.Function0<kotlin.Unit> declared in <root>.test8' type=kotlin.Function0<kotlin.Unit> origin=null
   FUN name:test9 visibility:public modality:FINAL <> () returnType:kotlin.Unit 
     BLOCK_BODY
       CALL 'public open fun run1 (r: java.lang.Runnable?): kotlin.Unit declared in <root>.J' type=kotlin.Unit origin=null