Profile evaluation should happen on the pty host, not extension host

[Tyriar]

Right now we fetch profiles on the extension host regardless of whether the window is local or remote, this would be better if it was moved to the pty host because:

• That's where similar functions related to terminal management are
• Initial profile fetching won't be blocked by the extension host's delayed start up time
• We can simplify the extension host implementation as it won't need to deal with profiles (default shell stuff should also be moved out eventually)

[Tyriar]

The variable resolver is used before validating the profile, this is currently not available on the pty service 🤔