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

idea/testData/quickfix/checkArguments/mixedNamedAndPositionalArgumentsMultiple.kt

@@ -0,0 +1,6 @@
+// "Add name to argument..." "true"
+fun f(a: Int, b: String = "b", c: String = "c") {}
+
+fun g() {
+    f(a = 10, <caret>"FOO")
+}