Improve Language Server performance

[TwitchBronBron]

There are significant slowdowns in the language server for larger apps. We should find ways to speed that up.

• maybe cache AST to speed up hovers/completions
• sometimes typing triggers too many validations. can we find a way to run the validation cycle less frequently? it's already debounced, but sometimes i see 3 runs instead of the expected 2

[TwitchBronBron]

I believe the majority of this has been addressed in #993