[HLSL] Implement floating literal suffixes (#87270)

This change implements the HLSL floating literal suffixes for half and
double literals. The PR for the HLSL language specification for this
behavior is https://github.com/microsoft/hlsl-specs/pull/175.

The TL;DR is that the `h` suffix on floating literals means `half`, and
the `l` suffix means `double`.

The expected behavior and diagnostics are different if native half is
supported. When native half is not enabled half is 32-bit so implicit
conversions to float do not lose precision and do not warn.

In all cases `half` and `float` are distinct types.

Resolves #85712