Note: The current implementation doesn't return optimal result for `fcmp
one/une x, +/-inf` since we don't handle this case in
https://github.com/llvm/llvm-project/pull/110891. Maybe we can make it
optimal after seeing some real-world cases.
This patch adds support for `ConstantFPRange::makeSatisfyingFCmpRegion`.
We only check the optimality for cases where the result can be
represented by a ConstantFPRange.
This patch also adds some tests for `ConstantFPRange::fcmp` because it
depends on `makeSatisfyingFCmpRegion`. Unfortunately we cannot
exhaustively test this function due to time limit. I just pick some
interesting ranges instead.
