[HLSL] Add abs library function

[HLSL] Add abs library function

This change exposes the abs library function for HLSL scalar types. Abs
is supported for all scalar, vector and matrix types. This patch only
adds a subset of scalar type support.

Fixes #57100 (https://llvm.org/pr57100)

The full documentation of the HLSL abs function is available here:
https://docs.microsoft.com/en-us/windows/win32/direct3dhlsl/dx-graphics-hlsl-abs

Reviewed By: bogner

Differential Revision: https://reviews.llvm.org/D131718