Primary reason for this is, that rendering meshpatches
every single time a translation is done, is very
expensive. So, we render it the first time and reuse it.

The way we do it is:

1) First we render the patch in scaled-up version of
   QImage, this helps us with loss of quality which is
   a consequence of `QPainter&` passed in
   `KoMeshGradientBackground::paint` as a scaled version.

2) We render the whole patch on QImage, not just the patch
   inside clipped region.

3) Then we render the QImage on QPainter in user coordinates
   i.e independent from the shape.

NOTE: One thing which has to be taken care of is, when we resize
the shape, the patch is resized as well. Which is one of the
expected behavior. But there is one more behavior, that is
the patches should not be scaled, which can help us with
having only selected portion of the patches in view.

Maniphest: T13101