[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

plugins/assign-plugin/testData/diagnostics/methodDeclaration.fir.kt

@@ -32,5 +32,5 @@ fun `should not report an error for assign return type for unannotated class`()
     data class IntTask(val input: IntProperty)
 
     val task = IntTask(IntProperty(42))
-    task.input = <!ASSIGNMENT_TYPE_MISMATCH!>42<!>
+    task.<!VAL_REASSIGNMENT!>input<!> = <!ASSIGNMENT_TYPE_MISMATCH!>42<!>
 }