[llvm] [KnownFPClass] Refine positive zero and NaN result classes for sqrt (PR #214987)

[via llvm-commits]

ZERICO2005 wrote:

All tests appear to pass okay if I cherry-pick this commit on this branch:
https://github.com/llvm/llvm-project/pull/214912 (which deals with `1.0 / sqrt(x)`

As in, this commit doesn't impact the `nofpclass` deductions for the other commit and etc

https://github.com/llvm/llvm-project/pull/214987