[llvm] [ValueTracking] Refactor `isKnownNonEqualFromContext` (PR #127388)

[Ramkumar Ramachandra via llvm-commits]

artagnon wrote:

> > Could you kindly add the NFC tag to the title? It's not obvious that this patch is an NFC, although the patch summary has an explanation.
> 
> It is not NFC. See [dtcxzyw/llvm-opt-benchmark#2121](https://github.com/dtcxzyw/llvm-opt-benchmark/pull/2121). The net effect is positive.

Could add some tests extracted from the diffs?

https://github.com/llvm/llvm-project/pull/127388