[llvm] [GISel] Add KnownFPClass Analysis to GISelValueTrackingPass (PR #134611)

[Matt Arsenault via llvm-commits]

https://github.com/arsenm approved this pull request.

lgtm with some nits. I don't think the unit tests fully cover all the cases here, but it's a pain to handle this in unit tests. It will be easier to do when this is wired up to something 

https://github.com/llvm/llvm-project/pull/134611