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

idea/testData/quickfix/checkArguments/mixedNamedAndPositionalArgumentsConstructor.kt

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