message: Deprecate toPromise.
  * Deprecate toPromise.
  Link to firstValueFrom or lastValueFrom instead.
  * Update Observable.ts
diff: @@ -348,8 +348,11 @@ export class Observable<T> implements Subscribable<T> {
  }
  /* tslint:disable:max-line-length */
  + /** @deprecated Deprecated use {@link firstValueFrom} or {@link lastValueFrom} instead */
  toPromise<T>(this: Observable<T>): Promise<T | undefined>;
  + /** @deprecated Deprecated use {@link firstValueFrom} or {@link lastValueFrom} instead */
  toPromise<T>(this: Observable<T>, PromiseCtor: typeof Promise): Promise<T | undefined>;
  + /** @deprecated Deprecated use {@link firstValueFrom} or {@link lastValueFrom} instead */
  toPromise<T>(this: Observable<T>, PromiseCtor: PromiseConstructorLike): Promise<T | undefined>;
  /* tslint:enable:max-line-length */
  @@ -363,6 +366,7 @@ export class Observable<T> implements Subscribable<T> {
  * @return A Promise that resolves with the last value emit, or
  * rejects on an error. If there were no emissions, Promise
  * resolves with undefined.
  + * @deprecated Deprecated use {@link firstValueFrom} or {@link lastValueFrom} instead
  */
  toPromise(promiseCtor?: PromiseConstructorLike): Promise<T | undefined> {
  promiseCtor = getPromiseCtor(promiseCtor);
  