fix/improve handling of mso-position-(horizontal|vertical)(-relative)

This is a squash of commits f6fa787 to e5bbc721 .

Change-Id: Ieb76ccb2fe8a425af3204de144021b7a731d0778
Reviewed-on: https://gerrit.libreoffice.org/11701
Reviewed-by: Miklos Vajna <vmiklos@collabora.co.uk>
Tested-by: Miklos Vajna <vmiklos@collabora.co.uk>