[gtk] (10 commits) Non-fast-forward update to branch wip/baedert/box2

[Timm Bäder <baedert src gnome org>]

The branch 'wip/baedert/box2' was changed in a way that was not a fast-forward update.
NOTE: This may cause problems for people pulling from the branch. For more information,
please see:

 https://wiki.gnome.org/Git/Help/NonFastForward

Commits removed from the branch:

  8f9492a... Stop using gtk_box_pack_end
  3ad7094... scalebutton: Stop relying on GtkBox's pack-type child prop
  be5e3b7... combobox: Stop using GtkBox's pack-type property
  ca3d12d... Stop using GtkBox's pack-type child prop in UI files
  01c2eff... dialog: Expose the content area as a separate GtkBox child
  a7db3ac... assistant: Fix button order in ui file
  dc82940... UI files stop using GtkBox prop
  50d5ce5... box: Remove pack-type child property
  3d994bf... testsuite: Remove box packing css node tests
  2ecdf81... box: Remove children list

Commits added to the branch:

  6412331... Stop using gtk_box_pack_end
  7ce09ab... scalebutton: Stop relying on GtkBox's pack-type child prop
  326be55... combobox: Stop using GtkBox's pack-type property
  b674d26... Stop using GtkBox's pack-type child prop in UI files
  7aff91b... dialog: Expose the content area as a separate GtkBox child
  a6a9e4f... assistant: Fix button order in ui file
  e1e4e32... box: Remove pack-type child property
  5b5b7ba... testsuite: Remove box packing css node tests
  8207545... box: Remove children list
  203309f... box: Simpify documentation