fdo#75757: remove inheritance to std::vector

from SfxDockArr_Impl, typedef'ing it as boost::ptr_vector<SfxDock_Impl>.

Change-Id: Ieb4f065a836cf9314464b9d5f53a09a95a974be8
Reviewed-on: https://gerrit.libreoffice.org/11707
Reviewed-by: David Tardon <dtardon@redhat.com>
Tested-by: David Tardon <dtardon@redhat.com>