Use modules instead of files for MPP diagnostic

Using files turned to be a bad idea, because people often
use the same name for files with expects and with corresponding actuals.

This commits disambiguiates ambiguous message for
AMBIGUOUS_ACTUALS/AMBGIUOUS_EXPECTS diagnostics by using modules instead
of files

^KT-32582 Fixed

idea/testData/multiModuleHighlighting/hierarchicalExpectActualMatching/duplicateExpectsExplicit/bottom/bottom.kt

@@ -1 +1 @@
-actual class <!AMBIGUOUS_EXPECTS("Actual class 'A'", "left.kt, right.kt")!>A<!>
+actual class <!AMBIGUOUS_EXPECTS("Actual class 'A'", "left, right")!>A<!>