[gtk] (3 commits) Non-fast-forward update to branch wip/chergert/builder-expose-object-fix

[Christian Hergert <chergert src gnome org>]

The branch 'wip/chergert/builder-expose-object-fix' 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:

  2818f68... builder: gracefully handle re-exposing builder object

Commits added to the branch:

  8fc618a... gtkbuilder: check for existing object before extending temp
  2f97ddc... gtkbuilder: update gtk_builder_extend_with_template_docs()
  069b0f2... gtkbuilder: update gtk_builder_expose_object() docs