[lld] [lld-macho] Implement ObjC category merging (-objc_category_merging) (PR #82928)

[Kyungwoo Lee via llvm-commits]

https://github.com/kyulee-com commented:

I've reviewed the code up to the parser + merger part so far, and please follow the rest code similarly. For the high-level comment:
 - please split another PR for symbol name change, which is unrelated.
 - `collectCategoryWriterInfoFromCategory` is a bit awkward. I'd suggest to set WriterInfo once somehow
 - Try to minimize passing a `output` variable and set them in the callee.
 

https://github.com/llvm/llvm-project/pull/82928