[libadwaita] (6 commits) Non-fast-forward update to branch wip/exalm/headerbars

[Alexander Mikhaylenko <alexm src gnome org>]

The branch 'wip/exalm/headerbars' 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:

  1bae0d4... stylesheet: Move the devel headerbar style to a nested widg
  47f2482... stylesheet: Restore a backdrop state for header bar
  7f67574... stylesheet: Tone down the devel style
  136ca2a... stylesheet: Add back a backdrop state for AdwTabBar

Commits added to the branch:

  2a28bce... stylesheet: Fix legacy dialog action area (*)
  64077db... stylesheet: Split dialog styles into a separate file (*)
  dad2e49... stylesheet: Move the devel headerbar style to a nested widg
  a7636b0... stylesheet: Restore a backdrop state for header bar
  736a9ea... stylesheet: Tone down the devel style
  37fc4cb... stylesheet: Add back a backdrop state for AdwTabBar

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