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/duplicateActualsExplicit/top/top.kt

@@ -1,3 +1,3 @@
 package foo
 
-expect class <!AMBIGUOUS_ACTUALS("Class 'A'", "bottom.kt, middle.kt")!>A<!>
+expect class <!AMBIGUOUS_ACTUALS("Class 'A'", "bottom, middle")!>A<!>