fix(core): make sure onStable runs in the right zone (#18706)

Make sure the callbacks to the NgZone callbacks run in the right zone
with or without the rxjs Zone patch -
1ed83d08ac.

PR Close #18706

packages/core/src/application_ref.ts

@@ -455,7 +455,11 @@ export class ApplicationRef_ extends ApplicationRef {
     });
 
     const isStable = new Observable<boolean>((observer: Observer<boolean>) => {
-      const stableSub: Subscription = this._zone.onStable.subscribe(() => {
+      // Create the subscription to onStable outside the Angular Zone so that
+      // the callback is run outside the Angular Zone.
+      let stableSub: Subscription;
+      this._zone.runOutsideAngular(() => {
+        stableSub = this._zone.onStable.subscribe(() => {
           NgZone.assertNotInAngularZone();
 
           // Check whether there are no pending macro/micro tasks in the next tick
@@ -468,6 +472,7 @@ export class ApplicationRef_ extends ApplicationRef {
             }
           });
         });
+      });
 
       const unstableSub: Subscription = this._zone.onUnstable.subscribe(() => {
         NgZone.assertInAngularZone();

packages/core/testing/src/component_fixture.ts

@@ -62,6 +62,9 @@ export class ComponentFixture<T> {
     this.ngZone = ngZone;
 
     if (ngZone) {
+      // Create subscriptions outside the NgZone so that the callbacks run oustide
+      // of NgZone.
+      ngZone.runOutsideAngular(() => {
         this._onUnstableSubscription =
             ngZone.onUnstable.subscribe({next: () => { this._isStable = false; }});
         this._onMicrotaskEmptySubscription = ngZone.onMicrotaskEmpty.subscribe({
@@ -96,6 +99,7 @@ export class ComponentFixture<T> {
 
         this._onErrorSubscription =
             ngZone.onError.subscribe({next: (error: any) => { throw error; }});
+      });
     }
   }