• HdyHeaderGroup:
  
  • Replace GtkHeaderBar as the child type by HdyHeaderGroupChild, and
    adjust the matching accessors. HdyHeaderGroupChild can hold a
    GtkHeaderBar, a HdyHeaderBar, and a HdyHeaderGroup, allowing to nest
    header groups.
    
  • Replace the 'focus' property by the 'decorate-all' property.
    
  • Add the update-decoration-layouts signal, used when nesting header
    groups.
    
• HdyHeaderBar:
  
  • Slight size request fix.
    
• Use the window node's radius instead of the decoration node's one to
  mask HdyWindow and HdyApplicationWindow.
  
• Make HdyAvatar, HdyHeaderGroup, HdySqueezer, HdyViewSwitcher,
  HdyViewSwitcherBar, HdyViewSwitcherTitle, and HdyWindowHandle final.
  
• Replace usage of (allow-none) by (nullable) or (optional).
  
• Translation updates:
  
  • Ukrainian