FIR checker: rework VAL_REASSIGNMENT_VIA_BACKING_FIELD(_ERROR)

compiler/testData/diagnostics/tests/backingField/LocalDeclarations.fir.kt

@@ -0,0 +1,34 @@
+// !LANGUAGE: +RestrictionOfValReassignmentViaBackingField
+
+class Outer {
+    val i: Int = 1
+        get() {
+            class Inner {
+                var i: Int = 2
+                    get() {
+                        field++
+                        return field
+                    }
+                val j: Int = 3
+                    get() {
+                        <!VAL_REASSIGNMENT_VIA_BACKING_FIELD_ERROR!>field<!> = 42
+                        return field
+                    }
+
+                fun innerMember() {
+                    <!VAL_REASSIGNMENT_VIA_BACKING_FIELD_ERROR!>field<!>++
+                }
+            }
+            return field
+        }
+
+    val j: Int = 4
+        get() {
+            fun local() {
+                <!VAL_REASSIGNMENT_VIA_BACKING_FIELD_ERROR!>field<!>++
+                <!VAL_REASSIGNMENT_VIA_BACKING_FIELD_ERROR!>field<!>++
+            }
+            local()
+            return field
+        }
+}

compiler/testData/diagnostics/tests/backingField/LocalDeclarations.kt

@@ -1,4 +1,3 @@
-// FIR_IDENTICAL
 // !LANGUAGE: +RestrictionOfValReassignmentViaBackingField
 
 class Outer {