The patch does multiple things:

1) Refactors KoShapeManager::paint() to use KisForest implementation
   to render shapes hierarchy. It is needed because we need to be able
   only a part of the shapes, and their parents might have filtering or
   masks. Theoretically, it is possible to implement this algorithm
   without KisForest, but it this case populateRenderSubtree(),
   buildRenderTree() and renderShapes() will be merged into a single
   function (or some counter-intuitive templated strategy), which would
   make the code hard to debug and maintain.

2) KoViewConverter is gone! Gone! You hear it?! It is gone!!! No more
   KoViewConverter in any rendering! :)
   Well, it is still used in the tools, but we can live with it for now.
   The main point, there is no ugly hacks in KoShape::absoluteTransformation()
   to correct shape's offset to let view scaling transform be applied
   *after* the shape. Now view tranform in applied *before* the shapes,
   right in KisShapeLayerCanvas (or the like).

The code touches a lot of code, so some testing is needed.

Things that were deprecated:
 * SVG-filtering rendering code was removed. It used an ugly hack to
   let it work on groups. It couldn't be kept after refactoring. When
   we implement it correctly, it should be just placed into renderShapes().

 * some features of ODF text and raster-based vector patterns might
   have become broken. But we have no way to test that :(

BUG:392242