Make LSP server use the new parser

[digama0]

• Depends on Implement frontend for HOLSource #1845

The LSP server in lsp-server.ML does not use the HOL parser currently. It should be updated to track intermediate states based on work in hol4-vscode.

This issue is complete when there is enough functionality in the LSP server to implement an editor mode for a new editor (including for example reimplementing the VSCode mode without writing any SML code).

[xrchz]

Attempting to capture some notes from @digama0 :

The LSP server needs to basically do what it's doing but instead of storing SML parse trees should store HOL parse trees, so it can serve requests for hovers etc.

lsp-server.ML should start to use (i.e. depend on) the code in holide.ML