[Enhancement] Nested Resources Folder

[Martinedo]

Summary

Allows us to make custom folders in the new Shared Resources.
In the .NET standup David showed how they intend to have one Shared Resources folder for every platform, which is super great.

But some platforms can't have subfolders in their own Resource folders (like Android\Resources\drawable), so it would be great if MAUIs project structure could support that.

Intended Use Case

Some apps require many images/resources and the best way to maintain them is categorising them into folders and subfolders.