[HLSL] Spec the c-style library architecture design for compiling shaders

[coopp]

This issue is to bottom out on the architecture for the c-style library for compiling shaders.

Details for this design may be in its own spec or added to the larger spec produced from this Issue #63631

A spec will be the result of this task that explains in more detail some of the following:

• What does the flow of compiling a shader look like?
• Is there an in-process solution?
• Is there an out of process solution?
• What libraries do consumers of this library link against?
• How is multi-threading addressed?