Overview

Adds custom LSP handlers for unison/editDefinition and unison/projectContext;
these will be used by the VS Code plugin (and possibly other LSP plugin implementations) tell UCM to add a definition to the specified file; and to fetch the currently connected LSP's project context respectively.

Implementation approach and notes

• Add the two new endpoints
• Make some tweaks to the underlying Edit Definition code to support non-ucm edit destinations.

Test coverage

Tested Manually

Loose ends

• We should publish a notification to the LSP clients when the project context changes so they can update too.
• We should properly jump to the definition in question if it's already in the file (there's currently a race condition here, since the actual edit to the file is performed separately from the request, but we can figure it out)
• Would be nice to have a search filter in the codebase panel, currently not feasible because UCM doesn't support it and namespaces are fetched on-demand
• Some way to switch projects from VS Code