Module aliasing: allow getting real module names via ImportPath getters

[elsh]

-Set real module names in ImportDecl
-Add getRealImportPath / getRealModulePath
-Print real module names in ASTDumper
Resolves rdar://83632921, rdar://83633109

[elsh]

@swift-ci smoke test

[xymus]

I noted a few nitpicks but overall the logic looks good to me.

[beccadax]

You might be able to talk me out of it, but I strongly suspect this should be implemented a little differently. Functionally, though, I think this is great other than the test quirks @xymus identified.

[elsh]

You might be able to talk me out of it, but I strongly suspect this should be implemented a little differently. Functionally, though, I think this is great other than the test quirks @xymus identified.

Thanks for the suggestions @beccadax! Addressed the rest of the comments.

[elsh]

@beccadax @xymus Thanks for reviewing! Let me know if there's anything else that needs to be addressed.

[elsh]

@swift-ci smoke test

[elsh]

@swift-ci smoke test

[elsh]

@swift-ci smoke test

[beccadax]

I have very, very minor comments on formatting and comment wording. (Some are mistakes in my previous suggestions—sorry about that.) These are all simple and mechanical, so I'm going to mark this "Approve" so that you don't need to ask for another review.

[elsh]

@swift-ci smoke test and merge