[FIR] Report VAL_REASSIGNMENT on assign to non-local vals

In this commit reporting on member properties in init section of class
  is not supported (see KT-55528)

^KT-55493 Fixed

compiler/testData/diagnostics/testsWithStdLib/contracts/controlflow/initialization/exactlyOnce/valIndefiniteInitialization.fir.kt

@@ -63,6 +63,6 @@ class InitializationForbiddenInNonInitSection {
     <!MUST_BE_INITIALIZED_OR_BE_ABSTRACT!>val x: Int<!>
 
     fun setup() {
-        myRun { x = 42 }
+        myRun { <!VAL_REASSIGNMENT!>x<!> = 42 }
     }
 }