Big change in quickfix tests: no stupid test data format with "before" and "after" file prefixes

idea/testData/quickfix/variables/changeToBackingField/bFRequired.kt.after

@@ -0,0 +1,8 @@
+// "Change reference to backing field" "true"
+class A() {
+    var a : Int
+    set(v) {}
+    init {
+        <caret>$a = 1
+    }
+}