EMF+: Implement line dashing.

Change-Id: I9eb21c0a8b5baa5b0080845f61b12fc65034d959
Reviewed-on: https://gerrit.libreoffice.org/6830
Reviewed-by: Andras Timar <andras.timar@collabora.com>
Tested-by: Andras Timar <andras.timar@collabora.com>