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

idea/testData/quickfix/modifiers/visibilityModifer2.kt.after

@@ -0,0 +1,8 @@
+// "Change visibility modifier" "true"
+open class A {
+    protected open fun run() {}
+}
+
+class B : A() {
+    <caret>protected override fun run() {}
+}