GNOME/gtkmm 4.21.2

on GNOME GitLab

Gsk:

• Add enum PorterDuff and Isolation.
  (Kjell Ahlstedt)
  

Gtk:

• Application: Call init_gtkmm_internals() in more constructors.
  (Kjell Ahlstedt) Issue #167 (Jean-Yves Lefort)
  
• Window: Add set/get_remove_on_hide().
  (Kjell Ahlstedt) Issue #166 (Jean-Yves Lefort)
  
• Picture: Add set/get/property_isolate_contents().
  
• PopoverBin: New widget.
  
• Snapshot: Add push_isolation() and push_composite().
  
• Svg: Add enum Svg::Features, load_from_resource(),
  set/get/property_features(), property_resource().
  Remove the Svg(const std::string& resource) constructor.
  Class Svg has not yet been included in a stable gtkmm release.
  (Kjell Ahlstedt)
  

Documentation:

• Gtk::GestureSingle, GestureClick: Update class descriptions.
  (Kjell Ahlstedt)
  

Build:

• Require gtk4 >= 4.21.4
  (Kjell Ahlstedt)