[HLSL] add cos library function

This change exposes the cos library function for HLSL,
excluding long, int, and long long doubles.
Cos is supported for all scalar, vector, and matrix types.

Long and long long double support is missing in this patch because those types
don't exist in HLSL. Int is missing because the cos function only works on floating type arguments.

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

Reviewed By: python3kgae

Differential Revision: https://reviews.llvm.org/D134921