Take over gtk-update-icon-cache from src:gtk+3.0

Not yet tested, and should go to experimental first.

@jbicha, do you think it's a good time to do this before the Ubuntu 24.04 deadline, or should we wait? We could either get this into testing before GTK 4.13/4.14, or entangle it with the transition to 4.13/4.14, or wait until after.

The practical difference is that in GTK4's update-icon-cache, we are not applying https://salsa.debian.org/gnome-team/gtk3/-/blob/debian/3.24.40-2/debian/patches/060_ignore-random-icons.patch?ref_type=tags (but according to upstream, it should no longer be necessary since 2008 anyway). We should check that the reproducer in https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=444285#41 no longer breaks it.