Versioning does not detect dependency when library references versioned library through is

[tjprescott]

Original issue: Azure/typespec-azure#2598

Playground

@versioned(MyVersions)
namespace MyLib {
  enum MyVersions {
    v1: "1",
    v2: "2",
  }

  // Correctly throws an error
  model MyFoo extends VersionedLib.Foo {};

  // All of these should trigger the error that @useDependency is required!
  model MyFoo is VersionedLib.Foo;
  alias MyFooAlias = VersionedLib.Foo;
  op FooOp is VersionedLib.FooOperation<{name: string}, string>;
  alias FooOperationAlias<TParam, TResponse> = VersionedLib.FooOperation<TParam, TResponse>;
}

It seems clear to me in this instances that if your library is using "is" or aliasing things from a versioned library, then you are taking a dependency on the source library, but existing logic does not pick that up.

[tjprescott]

Is seems I could get at the "is"ness of a Type by digging into the node, even though that seems to be frowned upon. However, detecting aliases will be trickier because they are not even included in navigateProgram, which is what the versioning library's $onValidate method relies on.

cc/ @nguerrera @timotheeguerin @bterlson @markcowl

[tjprescott]

Additionally, you can see in this playground that the problem isn't just that the validation doesn't detect the dependency...

...if I write my spec to reference things from a later version, even the "model extends" scenario is happy, even though all of these should throw an error!

[tjprescott]

This is blocked by #1810.

[tjprescott]

As an update, we don't need a solution for alias because it works automatically if the alias is actually used (as opposed to just declared).