[llvm] [LLVM] Create `lf_alias` nodes for `typedef` and `using` (PR #153936)

[via llvm-commits]

Walnut356 wrote:

(i apologize for the delays on this, i've been busy with a gsoc project 😅)

A small update: MSVC now seems to have a flag for this (`/d1typeAliasDebugRecords`, currently available on preview build tools. I checked and 14.52.36615 has it, but iirc it was added a month or two ago). I tried using Visual Studio 2026 v18.9.1, and the debugger was still unable to handle `LF_ALIAS`'d variables properly. This might be fixed in the insider version, but i haven't gotten around to testing it yet.

I'll still probably be busy for another month or so, so if anyone wants to yoink these changes and/or implement this themselves, feel free.

https://github.com/llvm/llvm-project/pull/153936