LSP startup time speedup and CWD fix

[ChrisPenner]

Overview

• This applies the UCM start-up time fix from regular UCM to the LSP
• The LSP will no longer report incorrect errors before the server is loaded, it'll just wait until it's ready.
• Fixes an issue where the LSP wasn't always being set to the correct 'current path'

Implementation notes

Like the UCM speedup, this skips loading the entire root-branch and instead just loads the current branch, which speeds things up a lot.

I swapped TVars which were being initialized with empty values, to TMVars that aren't filled until the LSP is loaded to avoid reporting incorrect errors.

Interesting/controversial decisions

Nah, straight-forward improvement.

Test coverage

I tried it out, we can dogfood on trunk for a bit.