src/vs/platform/telemetry/common/telemetryUtils.ts/combinedAppender
export function combinedAppender(...appenders: ITelemetryAppender[]): ITelemetryAppender {
	return {
		log: (e, d) => appenders.forEach(a => a.log(e, d)),
		flush: () => Promises.settled(appenders.map(a => a.flush()))
	};
}