[Test] Add ability to specify applicability of diagnostic to module or file

compiler/testData/diagnostics/tests/multimodule/duplicateClass/collectionMethodStub.kt

@@ -1,6 +1,6 @@
 // FIR_IDENTICAL
-// FILE: f1.kt
 // SKIP_TXT
+// FILE: f1.kt
 
 package kotlin
 
@@ -19,4 +19,4 @@ class C: MutableIterator<Int> {
         throw UnsupportedOperationException()
     }
 
-}
+}