[clang] [llvm] [mlir] [TableGen] Add const variants of accessors for backend (PR #106658)

[Rahul Joshi via cfe-commits]

jurahul wrote:

> > I propose the following next steps (once this is committed):
> 
> this timeline looks fine, do you also want to add `[[deprecated]]` once the PSA is out? Also, I can help on other LLVM TableGen backends if they haven't been updated.

Yeah, once all the upstream backends are migrated, we should mark the non-const ones deprecated. As for other backends, thanks for the offer! I have diffs for clang and mlir, so I am hoping I can do any other remaining ones as well (lldb and libc seem to have one). But if its start to get delayed, I can ping you for help.

https://github.com/llvm/llvm-project/pull/106658