Freeciv

Implement gtk4x-client citydlg prod list as GListStore. At first only 1) add the new implementation, 2) list old implementation as _depr, but 3) keep old implementation in use. This is to keep it clear in patch .diff what is the new implementation. Later ticket will switch the new implementation to use, and to remove the old one.

This one provides especially bad UI, but at this time the goal is just to get rid of constructs deprecated in latest versions of gtk4. During gtk3 -> gtk4 development the code didn't even compile at all times when doing similar work.