fix(aio): set focus back to search box on "escape"

For improved accessibility, the focus should be sent
back to the input box when we are displaying the
search results and the user hits ESC.

See #16005

aio/src/app/app.component.spec.ts

@@ -504,6 +504,15 @@ describe('AppComponent', () => {
         fixture.detectChanges();
         expect(searchBox.focus).toHaveBeenCalled();
       });
+
+      it('should set focus back to the search box when the search results are displayed and the escape key is pressed', () => {
+        const searchBox: SearchBoxComponent = fixture.debugElement.query(By.directive(SearchBoxComponent)).componentInstance;
+        spyOn(searchBox, 'focus');
+        component.showSearchResults = true;
+        window.document.dispatchEvent(new KeyboardEvent('keyup', { 'key': 'Escape' }));
+        fixture.detectChanges();
+        expect(searchBox.focus).toHaveBeenCalled();
+      });
     });
 
     describe('showing search results', () => {

aio/src/app/app.component.ts

@@ -268,6 +268,7 @@ export class AppComponent implements OnInit {
       // escape key
       if (this.showSearchResults) {
         this.hideSearchResults();
+        this.focusSearchBox();
       }
     }
   }