Fix incremental recompilation of JvmMultifileClass with top level function

See 53b584f and previous changes where this behavior was broken (this was
untested, however). Fixes EA-90065

compiler/frontend.java/src/org/jetbrains/kotlin/load/kotlin/incremental/IncrementalPackageFragmentProvider.kt

@@ -93,6 +93,9 @@ class IncrementalPackageFragmentProvider(
             )
         }
 
+        val multifileClassName: Name
+            get() = multifileClassFqName.shortName()
+
         override fun getMemberScope() = memberScope()
     }
 }