[InstCombine] Handle isNanOrInf idioms (#80414)

This patch folds:
```
(icmp eq (and (bitcast X to int), ExponentMask), ExponentMask) --> llvm.is.fpclass(X, fcInf|fcNan)
(icmp ne (and (bitcast X to int), ExponentMask), ExponentMask) --> llvm.is.fpclass(X, ~(fcInf|fcNan))
```
Alive2: https://alive2.llvm.org/ce/z/_hXAAF