[clang] [ObjC] Emit number, array, and dictionary literals as constants (PR #185130)

[Oliver Hunt via cfe-commits]

https://github.com/ojhunt requested changes to this pull request.

Mostly nits, but I think we should remove the separated key+object interfaces for the dictionary and just use pair<key,value>.

I'd also like the tests to include empty dictionary and array constants on targets that don't support constant initializers, do support them, and do support them but without supporting empty ones.

https://github.com/llvm/llvm-project/pull/185130