[clang] [HLSL][docs] Document hlsl.h in the HLSL docs (PR #84081)

[Damyan Pepper via cfe-commits]

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@@ -114,6 +114,44 @@ not re-targetable, we want to share the Clang CodeGen implementation for HLSL
 with other GPU graphics targets like SPIR-V and possibly other GPU and even CPU
 targets.
 
+hlsl.h
+------
+
+HLSL has an extensive library of functionality. This is similar to OpenCL and
+CUDA. The implementation approach for the HLSL library functionality draws from
+patterns in use by OpenCL and other Clang resource headers.
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damyanp wrote:

Would it be possible to have links to these similar headers for reference?

https://github.com/llvm/llvm-project/pull/84081