Introduce separate callee expression for when with subject variable

'Subject.Error' is redundant.
'Subject.None' can be an object.
'Subject#dataFlowValue' can be a lateinit property.

TODO: fix
- parsing local extension properties in 'when' subject
- parsing destructuring declarations in 'when' subject
- non-completed calls in nested 'when' with subject variable
- non-completed calls for subject variable in 'in' pattern

compiler/testData/diagnostics/tests/when/withSubjectVariable/shadowingOtherVariable.kt

@@ -2,10 +2,26 @@
 // !DIAGNOSTICS: -UNUSED_VARIABLE -UNUSED_PARAMETER
 
 fun foo(): Any = 42
+fun useInt(i: Int) {}
 
-fun test(y: Any) {
-    val z = when (val <!NAME_SHADOWING!>y<!> = foo()) {
-        42 -> "Magic: $y"
-        else -> "Not magic: $y"
+fun testShadowingParameter(y: Any) {
+    when (val <!NAME_SHADOWING!>y<!> = foo()) {
+        else -> {}
+    }
+}
+
+fun testShadowedInWhenBody(x: Any) {
+    when (val y = x) {
+        is String -> {
+            val <!NAME_SHADOWING!>y<!> = <!DEBUG_INFO_SMARTCAST!>y<!>.length
+            useInt(y)
+        }
+    }
+}
+
+fun testShadowinLocalVariable() {
+    val y = foo()
+    when (val <!NAME_SHADOWING!>y<!> = foo()) {
+        else -> {}
     }
 }

compiler/testData/diagnostics/tests/when/withSubjectVariable/shadowingOtherVariable.txt

@@ -1,4 +1,7 @@
 package
 
 public fun foo(): kotlin.Any
-public fun test(/*0*/ y: kotlin.Any): kotlin.Unit
+public fun testShadowedInWhenBody(/*0*/ x: kotlin.Any): kotlin.Unit
+public fun testShadowinLocalVariable(): kotlin.Unit
+public fun testShadowingParameter(/*0*/ y: kotlin.Any): kotlin.Unit
+public fun useInt(/*0*/ i: kotlin.Int): kotlin.Unit

compiler/testData/diagnostics/tests/when/withSubjectVariable/subjectVariableInIsPattern.kt

@@ -0,0 +1,8 @@
+// !LANGUAGE: +VariableDeclarationInWhenSubject
+// !DIAGNOSTICS: -UNUSED_VARIABLE -UNUSED_PARAMETER
+
+fun test(x: Any) {
+    when (val y = x) {
+        is String -> {}
+    }
+}

compiler/testData/diagnostics/tests/when/withSubjectVariable/subjectVariableInIsPattern.txt

@@ -0,0 +1,3 @@
+package
+
+public fun test(/*0*/ x: kotlin.Any): kotlin.Unit

compiler/testData/diagnostics/tests/when/withSubjectVariable/unsupportedVariableDeclarationsInWhenSubject.kt

@@ -2,8 +2,6 @@
 // !DIAGNOSTICS: -UNUSED_VARIABLE -UNUSED_PARAMETER
 // WITH_RUNTIME
 
-data class P(val x: Any, val y: Any)
-
 fun foo(): Any = 42
 fun String.bar(): Any = 42
 
@@ -15,26 +13,16 @@ fun testSimpleValInWhenSubject() {
 
 fun testValWithoutInitializerWhenSubject() {
     when (<!ILLEGAL_DECLARATION_IN_WHEN_SUBJECT!>val y: Any<!>) {
-        is String -> <!UNINITIALIZED_VARIABLE!>y<!>.<!UNRESOLVED_REFERENCE!>length<!>
+        is String -> <!UNINITIALIZED_VARIABLE, DEBUG_INFO_SMARTCAST!>y<!>.length
     }
 }
 
 fun testVarInWhenSubject() {
     when (<!ILLEGAL_DECLARATION_IN_WHEN_SUBJECT!>var y = foo()<!>) {
-        is String -> y.<!UNRESOLVED_REFERENCE!>length<!>
+        is String -> <!DEBUG_INFO_SMARTCAST!>y<!>.length
     }
 }
 
-fun testDestructuringInWhenSubject() {
-    when (val (y1, y2) = P(1, 2)) {
-    }
-}
-
-fun testExtensionValInWhenSubject() {
-    when (<!ILLEGAL_DECLARATION_IN_WHEN_SUBJECT!>val <!LOCAL_EXTENSION_PROPERTY, DEBUG_INFO_MISSING_UNRESOLVED!>String<!>.<!VARIABLE_WITH_NO_TYPE_NO_INITIALIZER!>len<!><!><!SYNTAX!><!> <!UNRESOLVED_REFERENCE!>get<!>(<!SYNTAX!><!>) = <!UNRESOLVED_REFERENCE!>bar<!>()<!SYNTAX!>)<!> <!UNUSED_LAMBDA_EXPRESSION!>{
-    }<!>
-}
-
 fun testDelegatedValInWhenSubject() {
     when (<!ILLEGAL_DECLARATION_IN_WHEN_SUBJECT!>val y by <!UNRESOLVED_REFERENCE!>lazy<!> { 42 }<!>) {
     }

compiler/testData/diagnostics/tests/when/withSubjectVariable/unsupportedVariableDeclarationsInWhenSubject.txt

@@ -2,21 +2,7 @@ package
 
 public fun foo(): kotlin.Any
 public fun testDelegatedValInWhenSubject(): kotlin.Unit
-public fun testDestructuringInWhenSubject(): kotlin.Unit
-public fun testExtensionValInWhenSubject(): kotlin.Unit
 public fun testSimpleValInWhenSubject(): kotlin.Unit
 public fun testValWithoutInitializerWhenSubject(): kotlin.Unit
 public fun testVarInWhenSubject(): kotlin.Unit
 public fun kotlin.String.bar(): kotlin.Any
-
-public final data class P {
-    public constructor P(/*0*/ x: kotlin.Any, /*1*/ y: kotlin.Any)
-    public final val x: kotlin.Any
-    public final val y: kotlin.Any
-    public final operator /*synthesized*/ fun component1(): kotlin.Any
-    public final operator /*synthesized*/ fun component2(): kotlin.Any
-    public final /*synthesized*/ fun copy(/*0*/ x: kotlin.Any = ..., /*1*/ y: kotlin.Any = ...): P
-    public open override /*1*/ /*synthesized*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
-    public open override /*1*/ /*synthesized*/ fun hashCode(): kotlin.Int
-    public open override /*1*/ /*synthesized*/ fun toString(): kotlin.String
-}