Relax nested type alias diagnostic

The warning about missing aliases for types nested in aliased types (#3940) is too strict in that it flags types which are exported at their declaration in another (exported) package. For example, see `azcore.ClientOptions` in [this review](https://apiview.dev/Assemblies/Review/61b05e90153942f68f3276de824c34e2?revisionId=581342650edd4a558d6c6b4edbdb6cdf&doc=False): `LogOptions` is exported at declaration in `azcore/policy`, so `azcore` shouldn't re-export it with an alias, making the warning spurious.

There are more complex cases. `azcore.ClientOptions` is an alias for `azcore/policy.ClientOptions` which has a field of type `Transporter`. `Transporter` is declared in `azcore/internal/exported` but exported from `azcore/policy` with an alias, so that doesn't deserve a warning either 🤯