Merge #8054

8054: Item movers r=matklad a=ivan770

Closes #6823

https://user-images.githubusercontent.com/14003886/111331579-b4f43480-8679-11eb-9af0-e4dabacc4923.mp4

Implementation issues:
- [ ] Most of items are non-movable, since _movability_ of any item has to be determined manually. Common ones are movable though
- [x] Cursor should move with the item

Co-authored-by: ivan770 <leshenko.ivan770@gmail.com>

crates/rust-analyzer/src/main_loop.rs

@@ -504,6 +504,7 @@ impl GlobalState {
             .on::<lsp_ext::HoverRequest>(handlers::handle_hover)
             .on::<lsp_ext::ExternalDocs>(handlers::handle_open_docs)
             .on::<lsp_ext::OpenCargoToml>(handlers::handle_open_cargo_toml)
+            .on::<lsp_ext::MoveItem>(handlers::handle_move_item)
             .on::<lsp_types::request::OnTypeFormatting>(handlers::handle_on_type_formatting)
             .on::<lsp_types::request::DocumentSymbolRequest>(handlers::handle_document_symbol)
             .on::<lsp_types::request::WorkspaceSymbol>(handlers::handle_workspace_symbol)