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

idea/testData/quickfix/override/nothingToOverride/addFunctionInLocalDeclaration.kt

@@ -0,0 +1,9 @@
+// "Add 'open fun f()' to 'A'" "true"
+open class A {
+}
+
+fun test() {
+    val some = object : A() {
+        <caret>override fun f() {}
+    }
+}