fix(ivy): ensure host bindings and host styling works on a root component (#28664)

Prior to this fix if a root component was instantiated it create host
bindings, but never render them once update mode ran unless one or more
slot-allocated bindings were issued. Since styling in Ivy does not make
use of LView slots, the host bindings function never ran on the root
component.

This fix ensures that the `hostBindings` function does run for a root
component and also renders the schedlued styling instructions when
executed.

Jira Issue: FW-1062

PR Close #28664

packages/core/test/acceptance/integration_spec.ts

@@ -0,0 +1,43 @@
+/**
+ * @license
+ * Copyright Google Inc. All Rights Reserved.
+ *
+ * Use of this source code is governed by an MIT-style license that can be
+ * found in the LICENSE file at https://angular.io/license
+ */
+import {Component, HostBinding} from '@angular/core';
+import {TestBed} from '@angular/core/testing';
+import {expect} from '@angular/platform-browser/testing/src/matchers';
+import {onlyInIvy} from '@angular/private/testing';
+
+describe('acceptance integration tests', () => {
+  onlyInIvy('[style] and [class] bindings are a new feature')
+      .it('should render host bindings on the root component', () => {
+        @Component({template: '...'})
+        class MyApp {
+          @HostBinding('style') public myStylesExp = {};
+          @HostBinding('class') public myClassesExp = {};
+        }
+
+        TestBed.configureTestingModule({declarations: [MyApp]});
+        const fixture = TestBed.createComponent(MyApp);
+        const element = fixture.nativeElement;
+        fixture.detectChanges();
+
+        const component = fixture.componentInstance;
+        component.myStylesExp = {width: '100px'};
+        component.myClassesExp = 'foo';
+        fixture.detectChanges();
+
+        expect(element.style['width']).toEqual('100px');
+        expect(element.classList.contains('foo')).toBeTruthy();
+
+        component.myStylesExp = {width: '200px'};
+        component.myClassesExp = 'bar';
+        fixture.detectChanges();
+
+        expect(element.style['width']).toEqual('200px');
+        expect(element.classList.contains('foo')).toBeFalsy();
+        expect(element.classList.contains('bar')).toBeTruthy();
+      });
+});