[gnome-shell] (16 commits) ...Port extensions app and portal to GTK4

[Marge Bot <marge-bot src gnome org>]

Summary of changes:

  eb0339e... shew: Use Xlib to set transient hint (*)
  c9c7629... extensions-app: Remove stray angle brackets (*)
  20a68a6... extensions-app: Set title on window instead of headerbar (*)
  8eb1792... extensions-app: Use consistent style for property names (*)
  ad6fbaa... extensions-app: Don't use deprecated margin-left/right prop (*)
  3af9091... extensions-app: Stop using :margin shortcut (*)
  1bb0e1b... extensions-app: Explicitly dispose window when removed (*)
  618762e... dbusServices/extensions: Minor cleanup (*)
  9d14b0c... dbusServices/extensions: Set title on window instead of hea (*)
  2189dc6... dbusServices/extensions: Use consistent style for property  (*)
  a450550... dbusServices/extensions: Stop using :margin shortcut (*)
  1016b91... dbusServices/extensions: Stop using GtkContainer API (*)
  9bb91ca... dbusServices/extensions: Stop using GtkToolbar (*)
  99a796e... dbusServices/extensions: Stop stacking frames (*)
  ba039bc... dbusServices/extensions: Remove event box (*)
  edd34c5... Port extensions app and portal to GTK4 (*)

(*) This commit already existed in another branch; no separate mail sent