Added 'change to backing field' fix

idea/testData/quickfix/variables/changeToBackingField/afterBFRequired.kt

@@ -0,0 +1,7 @@
+// "Change reference to backing field" "true"
+class A() {
+    val a : Int
+    {
+        <caret>$a = 1
+    }
+}

idea/testData/quickfix/variables/changeToBackingField/beforeBFRequired.kt

@@ -0,0 +1,7 @@
+// "Change reference to backing field" "true"
+class A() {
+    val a : Int
+    {
+        <caret>a = 1
+    }
+}