[IR] Fix file modules after actualization

When files from different IrModules are merged in IrActualizer
their IrModule link was not updated. This led to assuming them
as different modules, and incorrect internal visibility handling.

^KT-62623

compiler/ir/backend.common/src/org/jetbrains/kotlin/backend/common/actualizer/IrActualizer.kt

@@ -119,7 +119,9 @@ object IrActualizer {
     }
 
     private fun mergeIrFragments(mainFragment: IrModuleFragment, dependentFragments: List<IrModuleFragment>) {
-        mainFragment.files.addAll(0, dependentFragments.flatMap { it.files })
+        val newFiles = dependentFragments.flatMap { it.files }
+        for (file in newFiles) file.module = mainFragment
+        mainFragment.files.addAll(0, newFiles)
     }
 }