[llvm] [InstCombine] Canonicalize more saturated add variants (PR #100008)

[Rose Silicon via llvm-commits]

RSilicon wrote:

> This PR was pretty close to an acceptable state the last time I looked at it. Now you have once again added extra changes that nobody asked for, and moved it away from acceptance again.

And with that change, I fully exhausted all possible canonicalizations, well, minus actual variables but that will be for a follow-up PR

https://github.com/llvm/llvm-project/pull/100008