Fix pixel bleed in BorderImage

Keeping all patches of the border image in the same texture
with different sample points can cause parts of the border
to bleed over to the center patch. To rectify this, we
create a separate texture for each of the nine patches we
need, and separate image nodes.

To avoid applying antialiasing on the interior edges of the
border image, we introduce new antialiasing flags which can
be used to specify precisely which edges of the image should
be antialiased.

[ChangeLog][BorderImage] Fixed possible pixel bleed between
border patches and center patch in BorderImage.

Change-Id: Icc292b3969217320eecca99e79675316c42eab08
Task-number: QTBUG-35838
Reviewed-by: Gunnar Sletta <gunnar@sletta.org>