src/vs/workbench/api/browser/mainThreadNotebook.ts/MainThreadNotebooks/dispose
class MainThreadNotebooks:	dispose(): void {
		this._disposables.dispose();
		// remove all notebook providers
		for (const item of this._notebookProviders.values()) {
			item.disposable.dispose();
		}
		dispose(this._notebookSerializer.values());
	}