SI-7151 Emit final in bytecode for final inner classes.

As we did before a regression in 18efdedfb / SI-5676.

This commit tightens up the condition in which the FINAL
modifier is omitted; it now *only* does this for the module
classes of nested objects.
Merge pull request #2635 from retronym/ticket/7151

SI-7151 Emit final in bytecode for final inner classes.