Notebooks: Save cell connection name in cell metadata (#13208)

* save connection info in notebook metadata

* update attachTo dropdown based on saved alias

* add setting for saving connection (default=false)

* save/read cell connection name to/from metadata

* get started on toggling multi connection mode

* add activeConnection property to cell model

* add changeContext method for cell

* add comments

* add unit test for reading connection name

* save connection mode in metadata

* clean up code

* address PR comments

src/sql/workbench/contrib/notebook/test/electron-browser/cell.test.ts

@@ -1024,4 +1024,20 @@ suite('Cell Model', function (): void {
 		assert(!isEditMode);
 	});
 
+	test('Should read connection name from notebook metadata', async function () {
+		const connectionName = 'connectionName';
+		let notebookModel = new NotebookModelStub({
+			name: '',
+			version: '',
+			mimetype: ''
+		});
+		let contents: nb.ICellContents = {
+			cell_type: CellTypes.Code,
+			source: '',
+			metadata: { connection_name: connectionName }
+		};
+		let model = factory.createCell(contents, { notebook: notebookModel, isTrusted: false });
+		assert.equal(model.savedConnectionName, connectionName);
+	});
+
 });