lsp: Show graindoc on hover about grain HOT 1 OPEN

looking further into this, I think this will require a major rewrite of how Graindoc works.

Currently, we parse the file in a separate stage, and output everything for the file directly into a string.

We would need to:

• If we want this feature to be fast we either need to cache documentation or generate docs for each function separately (The former would probably be prefered as we resolve docs from other files)
• We would need to create a map between decl's and their doc info that can be easily accessed from the lsp

from grain.