fdo#62081: Add split menus to items in the style dropdown

I added buttons to the Style dropdown. Each button opens a menu.
So far I added "apply style" and "edit style" options.

Change-Id: I3b5c153a0674d06541d403bb0f34ec73418bb778
Reviewed-on: https://gerrit.libreoffice.org/11581
Reviewed-by: Samuel Mehrbrodt <s.mehrbrodt@gmail.com>
Tested-by: Samuel Mehrbrodt <s.mehrbrodt@gmail.com>