[gtk] (5 commits) Non-fast-forward update to branch wip/baedert/for-master

[Timm Bäder <baedert src gnome org>]

The branch 'wip/baedert/for-master' 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:

  bdc849a... Add pure and const annotations to various functions
  b7485d0... renderbackground: Avoid unnecessary work in snapshot_backgr
  9f38598... widget: Fix a transform leak in pick()

Commits added to the branch:

  a6e058a... Add pure and const annotations to various functions
  7fc2e1f... renderbackground: Avoid unnecessary work in snapshot_backgr
  e555651... widget: Restructure pick() a bit
  2ee9d7e... dimensionvalue: Add gtk_css_dimension_value_is_zero()
  fe0a612... cssboxes: Try to avoid doing work for rectangular boxes