fix(core): not inserting ViewContainerRef nodes when inside root of a component - #39599

… component (#39599)

When a `ViewContainerRef` is injected, we dynamically create a comment node next to the host
so that it can be used as an anchor point for inserting views. The comment node is inserted
through the `appendChild` helper from `node_manipulation.ts` in most cases.

The problem with using `appendChild` here is that it has some extra logic which doesn't return
a parent `RNode` if an element is at the root of a component. I __think__ that this is a performance
optimization which is used to avoid inserting an element in one place in the DOM and then
moving it a bit later when it is projected. This can break down in some cases when creating
a `ViewContainerRef` for a non-component node at the root of another component like the following:

```
<root>
  <div #viewContainerRef></div>
</root>
```

In this case the `#viewContainerRef` node is at the root of a component so we intentionally don't
insert it, but since its anchor element was created manually, it'll never be projected. This will
prevent any views added through the `ViewContainerRef` from being inserted into the DOM.

These changes resolve the issue by not going through `appendChild` at all when creating a comment
node for `ViewContainerRef`. This should work identically since `appendChild` doesn't really do
anything with the T structures anyway, it only uses them to reach the relevant DOM nodes.

Fixes #39556.

PR Close #39599