debt - soft remove NotebookCell#source

src/vs/vscode.proposed.d.ts

@@ -1392,8 +1392,6 @@ declare module 'vscode' {
 		readonly uri: Uri;
 		readonly cellKind: CellKind;
 		readonly document: TextDocument;
-		// API remove `source` or doc it as shorthand for document.getText()
-		readonly source: string;
 		language: string;
 		outputs: CellOutput[];
 		metadata: NotebookCellMetadata;

src/vs/workbench/api/common/extHostNotebook.ts

@@ -73,6 +73,7 @@ export class ExtHostCell extends Disposable implements vscode.NotebookCell {
 
 	get source() {
 		// todo@jrieken remove this
+		console.warn('USE cell.document.getText() instead');
 		return this._documentData.getText();
 	}