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

idea/testData/quickfix/createFromUsage/createVariable/property/valOnLibObject.kt.after

@@ -0,0 +1,8 @@
+// "Create extension property 'foo'" "true"
+// ERROR: Property must be initialized
+
+val Unit.foo: Int
+
+fun test() {
+    val a: Int = Unit.foo
+}