Run and Add Cell keybinding support (#3896)

- As part of this, fixed bug in the insertCell API where it didn't add to the end / failed if no cells existed

src/sql/workbench/services/notebook/common/notebookContext.ts

@@ -0,0 +1,15 @@
+/*---------------------------------------------------------------------------------------------
+ *  Copyright (c) Microsoft Corporation. All rights reserved.
+ *  Licensed under the Source EULA. See License.txt in the project root for license information.
+ *--------------------------------------------------------------------------------------------*/
+
+'use strict';
+
+import { RawContextKey } from 'vs/platform/contextkey/common/contextkey';
+
+/**
+ * Context Keys to use with keybindings for the notebook editor
+ */
+export const notebookEditorVisibleId = 'notebookEditorVisible';
+
+export const NotebookEditorVisibleContext = new RawContextKey<boolean>(notebookEditorVisibleId, false);