[HLSL] Poll Discourse and ping/revive older proposals for building a compiler library/compiler services to collect more information on the topic

[coopp]

A bit of research needs to be done by reading posts on https://discourse.llvm.org/ , discord, etc. to see how proposals for a compiler library were received. There were some old posts (around 2012) suggesting that a compiler library would be good to build. There was some push back and some suggestions, but it didn't go further.

This issue is to ping those threads and see what the current stance is on this issue. The results of this information gathering exercise will help construct a more concrete plan on the API plan.