Add in-memory strict language server

[heyimalex]

Implementation of approach that I described in #62. TL;DR: Create a strict LanguageService in memory and getSemanticDiagnostics from it for all strict files.

The create method in a plugin returns a LanguageService, and a LanguageService's entire view of the world is through a LanguageServiceHost. By proxying only getCompilationSettings on LanguageServiceHost to add strict: true and creating a new LanguageService from it, we create a perfect mirror of the stock LanguageService but with strict enabled.

Proxying the LanguageServiceHost was more difficult than the language server, as Object.keys(host) did not return all required methods. I tried grabbing the methods to proxy by walking up the prototype chain, but ultimately I couldn't figure it out; every time I'd be missing some other property and get some variant of a "cant access x on undefined" exception in the tsserver logs. Using a Proxy seems to have done the trick, and I'm successfully using this in my work repo now.

I also proxied dispose and cleanupSemanticCache as they seemed important to the LanguageService lifecycle. I have no idea if they're necessary.

[kamkry]

Thank you for your contribution! It's working well on my machine. Can you please bump up the version in your pull request? Great work!

[heyimalex]

Version bumped 👍

[KostkaBrukowa]

Published 2.2.2-beta.4 version with this change

[KostkaBrukowa]

published with 2.3.0 version on npm. Thanks for contribution!!!