[llvm] [ConstantFPRange] Implement `ConstantFPRange::makeAllowedFCmpRegion` (PR #110082)

[Matt Arsenault via llvm-commits]

arsenm wrote:

> iterating over all possible float values in `AnyOfValueInConstantFPRange` is not good for test times

It's supposed to be all fp8 values, which is a much smaller range


https://github.com/llvm/llvm-project/pull/110082