Merge #415

415: use LSP file system operations r=matklad a=vemoo

implements #131

I've replaced `source_file_edits` and `file_system_edits` with `workspace_edit` because [`WorkspacEdit`](https://docs.rs/languageserver-types/0.53.1/languageserver_types/struct.WorkspaceEdit.html) can represent both.

I only use `document_changes` because `changes` cannot represent file system operations.

But if the client doesn't have the `workspace.workspaceEdit.resourceOperations` capability `WorkspaceEdit` cannot replace the current `FileSystemEdit`. Can we assume that the client will support it?

I also adapted the extension code to make use of the new response type, but only for vscode, i don't know if changes have to be made for the emacs part.

Co-authored-by: Bernardo <berublan@gmail.com>