[HLSL] implement clamp intrinsic

[llvm-beanz]

Implement and expose the HLSL clamp intrinsic:

https://learn.microsoft.com/en-us/windows/win32/direct3dhlsl/dx-graphics-hlsl-clamp

AC:

• intrinsic is implemented
• Test to illustrate LLVM-IR generation

[llvmbot]

@llvm/issue-subscribers-clang-codegen

Author: Chris B (llvm-beanz)

Implement and expose the HLSL `clamp` intrinsic:

https://learn.microsoft.com/en-us/windows/win32/direct3dhlsl/dx-graphics-hlsl-clamp

AC:

• intrinsic is implemented
• Test to illustrate LLVM-IR generation