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

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

@@ -0,0 +1,8 @@
+// "Change function signature to 'fun f(a: Int)'" "true"
+trait A {
+    fun f(a: Int)
+}
+
+class B : A {
+    <caret>override fun f() {}
+}