Switch to teal-language-server

[pdesaulniers]

WIP

This PR replaces the extension's built-in language server with teal-language-server.

[Hedwig7s]

It doesn't seem to update the checks until the file is saved (or otherwise is a bit inconsistent)
Also requires nil parameters to be filled (and since teal-language-server is supposed to have optional parameters for all types I'll assume is a bug here for now)