[FIR] Add equality constraint from expected type for some synthetic function calls

This fixes some cases where we infer some type variable inside one
of the branches to Nothing instead of the expected type because Nothing
appeared in some other branch.

Specifically, we add an equality instead of a subtype constraint during
completion of calls to synthetic functions for if/when, try and !!.
We don't do it when the call contains a (possibly nested) elvis or is
inside the RHS of an assignment.
Otherwise, we would prevent some smart-casts.

#KT-65882 Fixed

compiler/testData/ir/irText/fakeOverrides/javastatic/staticOverrideOnKJ.fir.ir.txt

@@ -0,0 +1,64 @@
+FILE fqName:<root> fileName:/1.kt
+  CLASS CLASS name:A modality:FINAL visibility:public superTypes:[<root>.Java1]
+    $this: VALUE_PARAMETER INSTANCE_RECEIVER name:<this> type:<root>.A
+    CONSTRUCTOR visibility:public <> () returnType:<root>.A [primary]
+      BLOCK_BODY
+        DELEGATING_CONSTRUCTOR_CALL 'public constructor <init> () declared in <root>.Java1'
+        INSTANCE_INITIALIZER_CALL classDescriptor='CLASS CLASS name:A modality:FINAL visibility:public superTypes:[<root>.Java1]'
+    FUN FAKE_OVERRIDE name:bar visibility:public modality:OPEN <> () returnType:@[FlexibleNullability] kotlin.Any? [fake_override]
+      overridden:
+        public open fun bar (): @[FlexibleNullability] kotlin.Any? declared in <root>.Java1
+    FUN FAKE_OVERRIDE name:equals visibility:public modality:OPEN <> ($this:kotlin.Any, other:kotlin.Any?) returnType:kotlin.Boolean [fake_override,operator]
+      overridden:
+        public open fun equals (other: kotlin.Any?): kotlin.Boolean declared in <root>.Java1
+      $this: VALUE_PARAMETER name:<this> type:kotlin.Any
+      VALUE_PARAMETER name:other index:0 type:kotlin.Any?
+    FUN FAKE_OVERRIDE name:foo visibility:public modality:OPEN <> (t:@[FlexibleNullability] kotlin.Any?) returnType:kotlin.Unit [fake_override]
+      overridden:
+        public open fun foo (t: @[FlexibleNullability] kotlin.Any?): kotlin.Unit declared in <root>.Java1
+      VALUE_PARAMETER name:t index:0 type:@[FlexibleNullability] kotlin.Any?
+    FUN FAKE_OVERRIDE name:hashCode visibility:public modality:OPEN <> ($this:kotlin.Any) returnType:kotlin.Int [fake_override]
+      overridden:
+        public open fun hashCode (): kotlin.Int declared in <root>.Java1
+      $this: VALUE_PARAMETER name:<this> type:kotlin.Any
+    FUN FAKE_OVERRIDE name:toString visibility:public modality:OPEN <> ($this:kotlin.Any) returnType:kotlin.String [fake_override]
+      overridden:
+        public open fun toString (): kotlin.String declared in <root>.Java1
+      $this: VALUE_PARAMETER name:<this> type:kotlin.Any
+  CLASS CLASS name:B modality:FINAL visibility:public superTypes:[<root>.Java1]
+    $this: VALUE_PARAMETER INSTANCE_RECEIVER name:<this> type:<root>.B
+    CONSTRUCTOR visibility:public <> () returnType:<root>.B [primary]
+      BLOCK_BODY
+        DELEGATING_CONSTRUCTOR_CALL 'public constructor <init> () declared in <root>.Java1'
+        INSTANCE_INITIALIZER_CALL classDescriptor='CLASS CLASS name:B modality:FINAL visibility:public superTypes:[<root>.Java1]'
+    FUN FAKE_OVERRIDE name:bar visibility:public modality:OPEN <> () returnType:@[FlexibleNullability] kotlin.Any? [fake_override]
+      overridden:
+        public open fun bar (): @[FlexibleNullability] kotlin.Any? declared in <root>.Java1
+    FUN FAKE_OVERRIDE name:equals visibility:public modality:OPEN <> ($this:kotlin.Any, other:kotlin.Any?) returnType:kotlin.Boolean [fake_override,operator]
+      overridden:
+        public open fun equals (other: kotlin.Any?): kotlin.Boolean declared in <root>.Java1
+      $this: VALUE_PARAMETER name:<this> type:kotlin.Any
+      VALUE_PARAMETER name:other index:0 type:kotlin.Any?
+    FUN FAKE_OVERRIDE name:foo visibility:public modality:OPEN <> (t:@[FlexibleNullability] kotlin.Any?) returnType:kotlin.Unit [fake_override]
+      overridden:
+        public open fun foo (t: @[FlexibleNullability] kotlin.Any?): kotlin.Unit declared in <root>.Java1
+      VALUE_PARAMETER name:t index:0 type:@[FlexibleNullability] kotlin.Any?
+    FUN FAKE_OVERRIDE name:hashCode visibility:public modality:OPEN <> ($this:kotlin.Any) returnType:kotlin.Int [fake_override]
+      overridden:
+        public open fun hashCode (): kotlin.Int declared in <root>.Java1
+      $this: VALUE_PARAMETER name:<this> type:kotlin.Any
+    FUN FAKE_OVERRIDE name:toString visibility:public modality:OPEN <> ($this:kotlin.Any) returnType:kotlin.String [fake_override]
+      overridden:
+        public open fun toString (): kotlin.String declared in <root>.Java1
+      $this: VALUE_PARAMETER name:<this> type:kotlin.Any
+    FUN name:bar visibility:public modality:FINAL <> ($this:<root>.B) returnType:kotlin.String
+      $this: VALUE_PARAMETER name:<this> type:<root>.B
+      BLOCK_BODY
+        RETURN type=kotlin.Nothing from='public final fun bar (): kotlin.String declared in <root>.B'
+          CALL 'public final fun CHECK_NOT_NULL <T0> (arg0: T0 of kotlin.internal.ir.CHECK_NOT_NULL?): {T0 of kotlin.internal.ir.CHECK_NOT_NULL & Any} declared in kotlin.internal.ir' type=kotlin.String origin=EXCLEXCL
+            <T0>: kotlin.Nothing
+            arg0: CONST Null type=kotlin.Nothing? value=null
+    FUN name:foo visibility:public modality:FINAL <> ($this:<root>.B, t:kotlin.String) returnType:kotlin.Unit
+      $this: VALUE_PARAMETER name:<this> type:<root>.B
+      VALUE_PARAMETER name:t index:0 type:kotlin.String
+      BLOCK_BODY

compiler/testData/ir/irText/fakeOverrides/javastatic/staticOverrideOnKJ.fir.kt.txt

@@ -0,0 +1,24 @@
+class A : Java1 {
+  constructor() /* primary */ {
+    super/*Java1*/()
+    /* <init>() */
+
+  }
+
+}
+
+class B : Java1 {
+  constructor() /* primary */ {
+    super/*Java1*/()
+    /* <init>() */
+
+  }
+
+  fun bar(): String {
+    return CHECK_NOT_NULL<Nothing>(arg0 = null)
+  }
+
+  fun foo(t: String) {
+  }
+
+}

compiler/testData/ir/irText/fakeOverrides/javastatic/staticOverrideOnKJ.kt

@@ -1,4 +1,3 @@
-// FIR_IDENTICAL
 // TARGET_BACKEND: JVM
 
 // FILE: Java1.java