Remove duplicate identifiers in duplicate imports

[joe-matsec]

Resolves #2437.

This PR deduplicates import identifiers!

[joe-matsec]

Closing and resubmitting with my personal account 😅

[ljharb]

oof, duplicate PRs never go away :-/ can this be reopened so i can keep the two PRs in sync?

[joe-matsec]

Sorry about that.
Not sure I understand the idea behind keeping them both open but sure I can do that.

Edit: actually I'll just keep this one open in lieu of submitting another, it's not a big deal.

[ljharb]

If you want, I can rewrite the commit so it comes from your personal account :-)

(github keeps a "ref" for every PR that's ever been opened, that isn't fetched by default, although i fetch them all. as such, closing a PR leaves an orphaned ref, and it makes my git log harder to understand)

[ljharb]

@joe-matsec sorry for the late review! I rebased this, and a bunch of tests are failing. It's entirely possible that my attempt to conflict resolve has caused the problem - can you take a look?

We may also need to add some more test cases for duplicate inline type imports.

[joe-matsec]

@ljharb I think this is ready for another review when you have some time!
I'm not sure how to deal with Travis CI - Pull Request Action required after 4m — Build Errored but everything else is green in CI.

[joe-matsec]

@ljharb I rebased again and it looks like CI is still good, if you have some time to review. Thanks!