[gtk] (21 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:

  8464536... image: Remove some outdated comments
  817303a... image: Remove private struct from public header
  fd9879e... picture: Avoid some unnecessary signal connections
  5c292fc... buttonbox: Remove redundant if statement
  8157486... shortcutssection: Use a center box as footer
  d7111bf... tests: Remove flicker test
  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
  4ddbb8c... box: Remove children list
  67d2502... box: Simplify documentation
  5d502f7... box: Remove gtk_box_pack_end
  10ecc00... box: Remove gtk_box_pack_start
  4867d4c... migration guide: Add a paragraph about GtkBox's pack-type
  3aec971... colorchooser: Remove extra custom color
  3870e28... popover demo: Fix size-allocate callback signature

Commits added to the branch:

  f4ab75b... image: Remove private struct from public header
  cb205ef... picture: Avoid some unnecessary signal connections
  5bf6931... buttonbox: Remove redundant if statement
  a5210d0... shortcutssection: Use a center box as footer
  bc24f38... tests: Remove flicker test
  7178c53... Stop using gtk_box_pack_end
  d2c35b3... scalebutton: Stop relying on GtkBox's pack-type child prop
  d25efff... combobox: Stop using GtkBox's pack-type property
  cd167e4... Stop using GtkBox's pack-type child prop in UI files
  1dbe3f8... dialog: Expose the content area as a separate GtkBox child
  ac279d2... assistant: Fix button order in ui file
  7ba0ece... box: Remove pack-type child property
  7a21057... testsuite: Remove box packing css node tests
  8df2c55... box: Remove children list
  8d56271... box: Simplify documentation
  77fce70... box: Remove gtk_box_pack_end
  ecdd40c... box: Remove gtk_box_pack_start
  0d4ea46... migration guide: Add a paragraph about GtkBox's pack-type
  ab87baf... colorchooser: Remove extra custom color
  ae862db... popover demo: Fix size-allocate callback signature
  f454642... window: Fix state_flags_changed impl name