src/vs/workbench/contrib/extensions/browser/extensionsActions.ts/ActionWithDropDownAction/constructor
class ActionWithDropDownAction:	constructor(
		id: string, label: string,
		private readonly actionsGroups: ExtensionAction[][],
	) {
		super(id, label);
		this.extensionActions = flatten(actionsGroups);
		this.update();
		this._register(Event.any(...this.extensionActions.map(a => a.onDidChange))(() => this.update(true)));
		this.extensionActions.forEach(a => this._register(a));
	}