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

idea/testData/quickfix/variables/changeToPropertyName/inaccessibleBackingFieldQualified.kt.after

@@ -0,0 +1,6 @@
+// "Change '$a' to 'a'" "true"
+package foo
+val a = 5
+class A {
+    val b = foo.<caret>a
+}