[clang] Lex: add support for `i128` and `ui128` suffixes (PR #130993)

[Saleem Abdulrasool via cfe-commits]

compnerd wrote:

> > Take the opportunity to tighten up the code slightly by ensuring that we do not access out-of-bounds characters when lexing the token.
> 
> That's a nice touch :-)

😄

> Do we already have tests somewhere checking that we can codegen this, or do we need to add that?

I think that generally the `_BitInt` work should have given us the appropriate coverage. We use existing support for the Microsoft extension type `__int128` which has been there for a long time. I feel like we should have appropriate coverage already, but if you have a specific bit of coverage that you think would be good, I can try to integrate that.

https://github.com/llvm/llvm-project/pull/130993