fix(core): AsyncPipe now compatible with RxJS 7 (#41590)

Adds a fix to make sure that RxJS v7 Observable is compatible with AsyncPipe. This is a typings-only change.
For more information see: microsoft/TypeScript#43643

PR Close #41590

goldens/public-api/common/common.d.ts

@@ -3,9 +3,9 @@ export declare const APP_BASE_HREF: InjectionToken<string>;
 export declare class AsyncPipe implements OnDestroy, PipeTransform {
     constructor(_ref: ChangeDetectorRef);
     ngOnDestroy(): void;
-    transform<T>(obj: Subscribable<T> | Promise<T>): T | null;
+    transform<T>(obj: Observable<T> | Subscribable<T> | Promise<T>): T | null;
     transform<T>(obj: null | undefined): null;
-    transform<T>(obj: Subscribable<T> | Promise<T> | null | undefined): T | null;
+    transform<T>(obj: Observable<T> | Subscribable<T> | Promise<T> | null | undefined): T | null;
 }
 
 export declare class CommonModule {

packages/common/src/pipes/async_pipe.ts

@@ -7,7 +7,7 @@
  */
 
 import {ChangeDetectorRef, EventEmitter, OnDestroy, Pipe, PipeTransform, ɵisPromise, ɵisSubscribable} from '@angular/core';
-import {Subscribable, Unsubscribable} from 'rxjs';
+import {Observable, Subscribable, Unsubscribable} from 'rxjs';
 
 import {invalidPipeArgumentError} from './invalid_pipe_argument_error';
 
@@ -95,10 +95,14 @@ export class AsyncPipe implements OnDestroy, PipeTransform {
     }
   }
 
-  transform<T>(obj: Subscribable<T>|Promise<T>): T|null;
+  // NOTE(@benlesh): Because Observable has deprecated a few call patterns for `subscribe`,
+  // TypeScript has a hard time matching Observable to Subscribable, for more information
+  // see https://github.com/microsoft/TypeScript/issues/43643
+
+  transform<T>(obj: Observable<T>|Subscribable<T>|Promise<T>): T|null;
   transform<T>(obj: null|undefined): null;
-  transform<T>(obj: Subscribable<T>|Promise<T>|null|undefined): T|null;
-  transform<T>(obj: Subscribable<T>|Promise<T>|null|undefined): T|null {
+  transform<T>(obj: Observable<T>|Subscribable<T>|Promise<T>|null|undefined): T|null;
+  transform<T>(obj: Observable<T>|Subscribable<T>|Promise<T>|null|undefined): T|null {
     if (!this._obj) {
       if (obj) {
         this._subscribe(obj);