Support workspace symbols in language server

Would be nice to be able to navigate to types and functions across the whole workspace: https://microsoft.github.io/language-server-protocol/specifications/lsp/3.17/specification/#workspace_symbol

I had a brief look at the code and the immediate hurdle seems to be the routing within the language server. For document-level requests we determine the project to operate on from the document's file path. For workspace requests this path is simply not present.

I'd be happy to work on this if we can find a way around that!