[gtk] (19 commits) Non-fast-forward update to branch action-muxer-speedup

[Matthias Clasen <matthiasc src gnome org>]

The branch 'action-muxer-speedup' 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:

  342ac32... Speed up action muxer setup
  efacdd6... Speed up action muxer setup more
  8aa0a36... inspector: Remove action support temporarily
  d231e80... actionmuxer: Add some more api
  42e0eb9... actionmuxer: Port internal users
  110309a... actionmuxer: Stop implementing GActionGroup
  532436b... Add gtk_action_muxer_list_actions
  01dff4d... inspector: Make the actions tab work again
  5f0244a... actionmuxer: Create observed_actions and groups on demand
  0c01f67... actionmuxer: Use an array for accels
  8f246ba... actionmuxer: Update docs and clean up headers

Commits added to the branch:

  130bd59... docs: Add guidance about list model performance (*)
  75a30b1... windowhandle: Don't use an action muxer needlessly (*)
  b5e20a3... Merge branch 'matthiasc/for-master' into 'master' (*)
  86c7fce... Merge branch 'list-model-docs' into 'master' (*)
  378e594... Tweak the GTK_DEBUG=help output (*)
  95fc81c... inspector: Add a few more debug flags (*)
  5df1356... gsk: Remove an unused debug flag (*)
  0c15463... Merge branch 'matthiasc/for-master' into 'master' (*)
  aa76f7e... Speed up action muxer setup
  ab67a81... Speed up action muxer setup more
  07e8daf... inspector: Remove action support temporarily
  14bb121... actionmuxer: Add some more api
  4786a16... actionmuxer: Port internal users
  96d42cf... actionmuxer: Stop implementing GActionGroup
  9b294eb... Add gtk_action_muxer_list_actions
  14059af... inspector: Make the actions tab work again
  05e614f... actionmuxer: Create observed_actions and groups on demand
  ed92026... actionmuxer: Use an array for accels
  486fbce... actionmuxer: Update docs and clean up headers

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