Cell attachment cleanup tool improvement in diff editor (#161132)

* Move attachment out of custom metadata, prep for attachment clean up in diff editor

* recover attachments from dirty notebook document

* Allow metadata to be restored when content changed/reverted in nb diff editor

extensions/ipynb/src/ipynbMain.ts

@@ -35,9 +35,13 @@ export function activate(context: vscode.ExtensionContext) {
 		transientOutputs: false,
 		transientCellMetadata: {
 			breakpointMargin: true,
-			custom: false
+			custom: false,
+			attachments: false
+		},
+		cellContentMetadata: {
+			attachments: true
 		}
-	}));
+	} as vscode.NotebookDocumentContentOptions));
 
 	vscode.languages.registerCodeLensProvider({ pattern: '**/*.ipynb' }, {
 		provideCodeLenses: (document) => {