Alternative to fix RD-14971: remove inferrer threads and make inferre…

[miguelbranco80]

Remove threads from the inferrer. Therefore, it is no longer a RawService/does not need to be stopped. Since the inferrer is not "per user", change the code to instantiate it once, or rather, once per "RawSettings" The thread pool/caching is now part of the CompilerContext. It considers the language nodes as cache keys.