[Gtk] implement Maps

[lytico]

https://learn.microsoft.com/en-us/dotnet/maui/user-interface/controls/map?view=net-maui-8.0

Issue

Map implementation is completely missing

Control

Map

Handler

MapHandler.Gtk.cs

hints

https://github.com/judero01col/GMap.NET

running with GtkSharp, but with outdated GMap.NET: https://github.com/lytico/GMap.NET

https://github.com/QualitySolution/GMap.NET/tree/master/GMap.NET.GtkSharp

GTK2!:
https://github.com/lytico/maui/tree/lytico/merge/main240321/src/Compatibility/Maps/src/Gtk2

other gtk.maps projects

https://github.com/nzjrs/osm-gps-map

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

see also:
lytico#32