[llvm] [LVI][CVP] propagates `undef` to range and `abs` (PR #68190)

[via llvm-commits]

DianQK wrote:

> The way you are propagating undef here is basically as if it were poison, but this doesn't match its semantics. `zext CR|undef` does not result in `CR.zext()|undef`, because the top bits are guaranteed to be zero even if the input is undef.

Thanks for pointing that out. Yes! This is the better approach.

For a better review and commit history, I will submit a separate PR for `abs`. And test cases for the new abs may depend on the PR.

https://github.com/llvm/llvm-project/pull/68190