FIR checker: report val reassignment

compiler/testData/diagnostics/tests/when/ExhaustiveValOverConditionalInit.fir.kt

@@ -16,8 +16,8 @@ fun foo(a: Boolean, b: Boolean): Int {
         x = 1
     }
     when (b) {
-        true -> x = 2
-        false -> x = 3
+        true -> <!VAL_REASSIGNMENT!>x<!> = 2
+        false -> <!VAL_REASSIGNMENT!>x<!> = 3
     }
     return x
 }
@@ -28,7 +28,7 @@ fun bar(a: Boolean, b: Boolean): Int {
         x = 1
     }
     when (b) {
-        false -> x = 3
+        false -> <!VAL_REASSIGNMENT!>x<!> = 3
     }
     return <!UNINITIALIZED_VARIABLE!>x<!>
 }

compiler/testData/diagnostics/tests/when/withSubjectVariable/reassignmentToWhenSubjectVariable.fir.kt

@@ -1,10 +0,0 @@
-// !LANGUAGE: +VariableDeclarationInWhenSubject
-// !DIAGNOSTICS: -UNUSED_VARIABLE -UNUSED_PARAMETER -UNUSED_VALUE
-
-fun foo(): Any = 42
-
-fun test1(x: Any) {
-    when (val y = foo()) {
-        is String -> y = ""
-    }
-}

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

@@ -1,3 +1,4 @@
+// FIR_IDENTICAL
 // !LANGUAGE: +VariableDeclarationInWhenSubject
 // !DIAGNOSTICS: -UNUSED_VARIABLE -UNUSED_PARAMETER -UNUSED_VALUE