[llvm] [Support] Add decodeULEB128AndInc/decodeSLEB128AndInc (PR #85739)

[Adrian Prantl via llvm-commits]

https://github.com/adrian-prantl approved this pull request.

I've been toying with the idea of moving the decoder function into the .cpp file, and maybe having two entry points for error / no errors to further speed up decoding, and this seems to get us closer to that goal.

https://github.com/llvm/llvm-project/pull/85739