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

idea/testData/quickfix/override/overriddingMultipleFinalMethods.kt

@@ -0,0 +1,20 @@
+// "Make 'foo' in A, X and Y open" "true"
+open class A {
+    fun foo() {}
+}
+
+trait X {
+    final fun foo() {}
+}
+
+trait Y {
+    final fun foo() {}
+}
+
+trait Z {
+    fun foo() {}
+}
+
+class B : A(), X, Y, Z {
+    override<caret> fun foo() {}
+}