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

[via llvm-commits]

Nerixyz wrote:

> But not in Visual Studio or with the C/C++ extension for vscode.

That's very unfortunate. However, I still think it would be great if LLVM (and eventually LLDB) could at least read the type record. So what about the following plan:

1. Add `LF_ALIAS` to LLVM's CodeView support and llvm-pdbutil. Then, test it using yaml2pdb/pdb2yaml. If necessary, the produced PDB could be manually verified with `cvdump` or similar tools that already understand the record.
2. Update LLDB's native PDB plugin.
3. Once the VS debugger properly supports the record, emit this record in LLVM. Might still need to be behind some flag(?)

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