[HLSL] implement the `isinf` intrinsic (#84927)

This change implements part 1 of 2 for #70095
- `hlsl_intrinsics.h` - add the `isinf` api
- `Builtins.td` - add an hlsl builtin for `isinf`.
- `CGBuiltin.cpp` add the ir generation for `isinf` intrinsic.
- `SemaChecking.cpp` - add a non-math elementwise checks because this is
a bool return.
- `IntrinsicsDirectX.td` - add an `isinf` intrinsic.

`DXIL.td` lowering is left, but changes need to be made there before we
can support this case.