Z-Index was not handledin LO for vml.
I have made the changes to handle that using aGrabBag.

Change-Id: I2af3b2974c8eb699bc6a7b743dc438584d6517ac
Reviewed-on: https://gerrit.libreoffice.org/8833Reviewed-by: Miklos Vajna <vmiklos@collabora.co.uk>
Tested-by: Miklos Vajna <vmiklos@collabora.co.uk>