Add completion support for locals

[vinistock]

Motivation

Add completion support for locals.

Implementation

There are two parts to the implementation:

1. We need to start remembering the full nesting nodes inside node context. This is needed because we need to traverse the exact surrounding scopes to determine which locals are available inside the target
2. Started including local variables as part of method completion. This may seem counter intuitive, but until you finish typing the entire name of the local variable, it is actually considered as a method call (since Prism hasn't yet matched it to a local)

Automated Tests

Added tests.

Manual Tests

Launch the LSP on this branch and verify you get locals as completion suggestions.

Screen.Recording.2024-07-02.at.5.55.03.PM.mov

[amomchilov]

Neat!

[amomchilov]

Future feature idea: fuzzy matching?

[vinistock]

I think VS Code already does that. There are two ways to return completion items: a complete list or an incomplete one.

For the incomplete one, the server is responsible for re-computing all candidates one very keystroke (in this scenario, fuzzy matching on the server would indeed be very nice).

For the complete one, we return all matches for the first character and the client (VS Code) will handle the fuzzy matching on all candidates, which is what we currently do for performance reasons. Anything we can delegate to the client means less work for the server.