[FE 1.0] Migrate most of warning/error pairs to DiagnosticFactoryForDeprecation

compiler/testData/diagnostics/tests/controlFlowAnalysis/backingFieldInsideGetter_before.kt

@@ -8,7 +8,7 @@ import java.util.HashSet
 val a: MutableSet<String>? = null
     get() {
         if (a == null) {
-            <!VAL_REASSIGNMENT_VIA_BACKING_FIELD!>field<!> = HashSet()
+            <!VAL_REASSIGNMENT_VIA_BACKING_FIELD_WARNING!>field<!> = HashSet()
         }
         return a
     }
@@ -17,7 +17,7 @@ class R {
     val b: String? = null
         get() {
             if (b == null) {
-                <!VAL_REASSIGNMENT_VIA_BACKING_FIELD!>field<!> = "b"
+                <!VAL_REASSIGNMENT_VIA_BACKING_FIELD_WARNING!>field<!> = "b"
             }
             return b
         }