To get the anti-aliased polygon we draw a anti-aliased line around
every trapezoid. This works fine until we draw a transparent
polygon where the lines become visible because of blending. A much
better and faster way is to just draw the polygon outline with
anti-aliased lines. This is done with this commit.

Change-Id: Ice50e5eb3343f2c5d51ade8ad0e170043541f0ff
Reviewed-on: https://gerrit.libreoffice.org/27611Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Tomaž Vajngerl <quikee@gmail.com>