[clang-tools-extra] Add Objective-C support to include-cleaner's AST walker. (PR #211119)

[Nico Weber via cfe-commits]

https://github.com/nico approved this pull request.

lgtm, thanks!

@kadircet @hokein in case you have anything to add. If not, I'll merge this in a few days :)

https://github.com/llvm/llvm-project/pull/211119