fix(core): cleanup DOM elements when root view is removed (#37600)

Currently when bootstrapped component is being removed using `ComponentRef.destroy` or `NgModuleRef.destroy` methods, DOM nodes may be retained in the DOM tree. This commit fixes that problem by always attaching host element of the internal root view to the component's host view node, so the cleanup can happen correctly.

Resolves #36449.

PR Close #37600

packages/core/testing/src/r3_test_bed.ts

@@ -332,7 +332,7 @@ export class TestBedRender3 implements TestBed {
 
   createComponent<T>(type: Type<T>): ComponentFixture<T> {
     const testComponentRenderer = this.inject(TestComponentRenderer);
-    const rootElId = `root-ng-internal-isolated-${_nextRootElementId++}`;
+    const rootElId = `root${_nextRootElementId++}`;
     testComponentRenderer.insertRootElement(rootElId);
 
     const componentDef = (type as any).ɵcmp;