New built-in decorator to mark a known model

Kinda a way to make a model nominal.

There is a few models that we have to have custom decorators to be able to check if it is that model. You cannot just do assignment check as it would work with structure comparaison.

For example we have `@embedingVector` to mark a special vector array. It might be better if we had a standard way to resolve those.

Something like

```
@nominal("Azure.Core.EmbeddingVector")
model EmbeddingVector is Array
```