fdo#74681: quick help may be used as accessible text

In case a tool box item does not contain some text to be used as the
accessible item name, use the quick help text.

Change-Id: I9caadb0989729787d8572f4007652bcab02b0412
(cherry picked from commit 9b2582064882bb1a1caea72fe7754b8872a16413)
Reviewed-on: https://gerrit.libreoffice.org/9900
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>