[niepce] (34 commits) ...Port to Gtk4

[Hubert Figuière <hub src gnome org>]

Summary of changes:

  bcb3221... gtk4: initial port (*)
  88319a9... gtk4: Fix the layout of the top inner UI (*)
  7a1912b... gtk4: Fix main menu position (regression) (*)
  36ae0ba... gtk4: fix critical warning about gesture (*)
  25d92ff... gtk4: fix the workspace treeview display (*)
  7e9cc0f... gtk4: Fix debug build (*)
  10942ea... gtk4: Fix dialogs (*)
  9d623c1... gtk4: use snapshot more in the cell renderer (*)
  2924d12... gtk4: set canvas widget expand (*)
  d5ba72c... gtk4: fix hscale expand (*)
  40f40ef... gtk4: Fix Rust widget sample (*)
  8d7d7f8... gtk4: Fix context menus (*)
  3531802... gtk4: fix the thumbnail display (*)
  c2fecda... rust: Fix clippy warnings (*)
  9338a6e... gtk4: Fix the context menu on ImageGridView (*)
  4a8e87c... gtk4: Fix spacing of the main UI (*)
  1d7de0f... Update flatpak manifest (*)
  34d8202... gtk4: Fix about dialog (*)
  567e76d... gtk4: Fix edit label dialog (*)
  ad94d9c... gtk4: Fix confirm dialog (*)
  035e174... gtk4: don't crash on create folder (*)
  9adecbd... libraryclient: the client no longer need mut (*)
  5406309... Use sigc for trackables to avoid crash (*)
  33454a7... gtk4: fix create folder (*)
  bb67c67... gtk4: Fix import directory (*)
  64499ff... gtk4: replace osm-gps-map with shumate (*)
  14e5e20... rust: fix typo in debug message (*)
  18f34ab... library: upgrade schema to 10 (*)
  41c6646... library: when writing an XMP, add it to the bundles
  ee2a237... Update README for gtk4
  e6e68ac... gtk4: Fix widget-test
  2a5d3ea... gtk4: Fix crash
  6219ac3... gtk4: context menus don't have arrows
  5bf4792... Port to Gtk4

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