GTK4 support

[jonathonf]

Even today, Numix remains a bastion of clean, minimal design in a world of bland material design-alikes and macOS-derivatives.

Please consider coming back to this theme and adding GTK4 support. If that would require some sort of sponsorship let me know.

I strongly support this. Fedora36 with Gnome42 is coming (I am running the dev version already) and GTK4 apps stick out like a sore thumb among the beautiful looking Numix-styled applications.

[cocoa1231]

I would also love to see this!

[noggynoggy]

Is there any progress with this? 😃