[llvm] [KnownBits] Add KnownBits::add and KnownBits::sub helper wrappers. (PR #99468)

[Simon Pilgrim via llvm-commits]

RKSimon wrote:

I've added NSW/NUW arguments that default to false - although this means we can't easily use these in llvm::function_ref callbacks anymore

https://github.com/llvm/llvm-project/pull/99468