[Select] Expose `Portal` part like in `Dialog`

[christophlocher]

There have been several improvements made to expose the Portal used by components to allow for more control over the layering: #1302 #1303 #1304 #1305 #1306

This would also be great for the Select component.

---

PS: Thanks for building this great library, it is greatly appreciated!

[benoitgrelard]

Hi @ChristophLabacher,

Thanks for the kind words. This has also been done for Select already as part of #1459.