Edit book using drag and drop (#16906)

- Use the onDrop method for moving notebooks/sections in the Notebooks Tree View.
- Allow multi selection in tree view
- Modify notebook commands to only show when a single tree item is selected.

extensions/notebook/src/telemetry.ts

@@ -21,5 +21,6 @@ export enum NbTelemetryActions {
 	PinNotebook = 'NotebookPinned',
 	OpenNotebookFromBook = 'NotebookOpenedFromBook',
 	MoveNotebook = 'MoveNotebook',
+	DragAndDrop = 'DragAndDrop'
 }