ToolBarManager already supported addon buttons because of the toolbar merging feature. Besides the cleanup, this gives access to addon devs to all toolbar features like aliases or style buttons. Change-Id: I7adf830ac71c7f5354a924d60a531d8001e37571 Reviewed-on: https://gerrit.libreoffice.org/c/core/+/101071 Tested-by: Jenkins Reviewed-by: Maxim Monastirsky <momonasmon@gmail.com>