[BUGFIX release] Fix types for getOwner and GlimmerComponent

[chriskrycho]

The type for getOwner() is intended to return Owner in cases where we can safely assume that the object instance does in fact have an owner. However, as pointed out by @bendemboski today in Discord, this does not work correctly in the scenario where we have a component which actually has a signature defined:

class Example extends Component<{ Args: { anyWillDo: true } }> {
  method() {
    getOwner(this); // should be `Owner`, not `| undefined`
  }
}

Presently, we return Owner | undefined instead.

This PR fixes this by using GlimmerComponent<any> instead of plain GlimmerComponent, since the latter resolves to the default GlimmerComponent<unknown>, which ends up being too narrow to resolve correctly with getOwner when any actual signature is applied.

As a bonus, rename FrameworkObject in this context to the somewhat more verbose KnownFrameworkObject, which avoids a conflict with the actual FrameworkObject type used internally.

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Additionally: The type for getOwner() is technically unsafe, but this unsafety is one which end users will rarely hit in practice and, courtesy of Ember's current types, is unavoidable if getOwner(someService) is to correctly return Owner instead of Owner | undefined.

The Typed Ember folks have discussed this point at some length, but I realized on looking at this to make the changes in the first two commits for this PR that we didn't have it committed to the code base anywhere, so this PR also introduces a long comment explaining it. When we switch from preview to stable types, this comment should come along!

[wagenet]

I don't love this, but it's probably worth it to avoid having to assert every time we getOwner.

[chriskrycho]

Yeah. I’m going to merge with this as is, but I’m also going to do a follow-on which actually makes it safer, based on something I came up with chatting @dfreeman this morning.