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

[Fangrui Song via llvm-commits]

MaskRay wrote:

Sorry, just saw the discussion. Added #90006

(I believe removing default arguments isn't a lot useful as users can always use the existing decodeULEB128 with default arguments)

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