[FEATURE] Add TypeScript support for looking up controllers in DI registry

[littleredridingfox]

This PR enables controller type discovery through Owner::lookup method:

declare module '@ember/controller' {
  interface Registry {
    foo: FooController;
  }
}

const fooController = this.owner.lookup('controller:foo'); // TS resolves fooController's type as FooController.
const barController = this.owner.lookup('controller:bar'); // If not specified via Registry interface, will resolve type as Controller | undefined

Complementary PR to @types/ember__controller: DefinitelyTyped/DefinitelyTyped#66067

[chriskrycho]

We'll discuss, and I expect we'll merge this, since we have the corresponding APIs covered elsewhere. I want to say, however: I didn't implement it for a reason, which is that folks should absolutely move away from using controller lookup like this, for a host of reasons, most of all that controller lifecycle is weird and that 99% of things people do with controllers should be done with routes, services, and components instead. (The only real exception is query param management!) Like I said, though: since the API is there, I expect we will likely support it.

While we are discussing, folks should be aware that you can implement this yourself in any app or addon without needing official support. (This is the other part of the reason I did not prioritize implementing it when adding general DI registry support for lookup.)

[chriskrycho]

I'm making one tweak to the docs and then we can land this; note that I'm also tweaking what it lands as—a feature, not a bug fix. The previous types were correct here—they would never have caused a runtime error—so this is best flagged as a new capability.

Do please consider migrating away from controller injections to using service injections or passing arguments instead, as that is much more aligned with where the framework is headed!