[llvm] [GlobalISel] Add G_ABS computeKnownBits, add computeNumSignBitsImpl to work ComputeKnownBitsCache assertions (PR #154413)

[Pragyansh Chaturvedi via llvm-commits]

r41k0u wrote:

Thanks. This is much more concise now. I have rebased over main and  removed the cache related changes

https://github.com/llvm/llvm-project/pull/154413