[libadwaita] (3 commits) Non-fast-forward update to branch wip/exalm/borders-fixes

[Alexander Mikhaylenko <alexm src gnome org>]

The branch 'wip/exalm/borders-fixes' 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:

  c2727f0... header-bar: Adjust heights
  645c785... demo: Simplify the split header bar layout

Commits added to the branch:

  e7b03bd... stylesheet: Support headerbar.flat (*)
  9a7040d... header-bar: Adjust heights
  217fd71... demo: Simplify the split header bar layout

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