5917: Add a command to open docs for the symbol under the cursor r=matklad a=zacps
#### Todo
- [ ] Decide if there should be a default keybind or context menu entry
- [x] Figure out how to get the documentation path for methods and other non-top-level defs
- [x] Design the protocol extension. In future we'll probably want parameters for local/remote documentation URLs, so that should maybe be done in this PR?
- [x] Code organisation
- [x] Tests
Co-authored-by: Zac Pullar-Strecker <zacmps@gmail.com>
Return an error with a meaningful message for requests to
`textDocument/rename` if the operation cannot be performed.
Pass errors raised by rename handling code to the LSP runtime.
As a consequence, the VS Code client shows and logs the request
as if a server-side programming error occured.
Resolves https://github.com/rust-analyzer/rust-analyzer/issues/3981
This removes all markdown when the client does not support the markdown MarkupKind
Otherwise the output on the editor will have some markdown boilerplate, making it less readable
This seems like a better factoring logically; ideally, clients shouldn't touch
`set_` methods of the database directly. Additionally, I think this
should remove the unfortunate duplication in fixture code.
