[gtk] (4 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:

  ade8ae3... dimensionvalue: Add gtk_css_dimension_value_is_zero()
  591579b... cssboxes: Try to avoid doing work for rectangular boxes
  e734db4... cssdimensionvalue: Remove an outdated comment
  f5402ea... gsk: Remove some unused defines

Commits added to the branch:

  9ad5ed4... dimensionvalue: Add gtk_css_{dimension,corner}_value_is_zer
  3878c0b... cssboxes: Try to avoid doing work for rectangular boxes
  d94c6bb... cssdimensionvalue: Remove an outdated comment
  c627013... gsk: Remove some unused defines