New Library: Panel

[brisingraerowing]

Panel is an IDE-style docking component for GTK 4.

https://gitlab.gnome.org/GNOME/libpanel

[badcel]

This is a duplicate of #535.

The big problem is that libpanel is not part of the GNOME SDK currently: gircore/gir-files#266

So there would need to be another way of fetching gir files which is a major undertaking (#744) or every user must create the bindings manually.

But building it manually requires checking out the code, as the generator is not yet a nuget: #1078

So we are a bit stuck here. I think going the generator route is the best way forward currently. Any help for this would be greatly appreciated.