* make SimpleText::add_run accept glyph_transform and style parameters so it doesn't unconditionally do oblique strokes
* replace fill/stroke methods on DrawGlyphs with a single draw method that accepts either fill or stroke styles
* update peniko rev to access the new style types used above
* for now, change glyph cache to only cache non-zero fills. Prior to this, style was ignored in the key which could lead to incorrect rendering.
Added two scenes that demonstrate conflation artifacts as described in
https://github.com/linebender/vello/issues/49. The first scene
demonstrates adjacent triangles and rects that belong to the same path
and use opposite winding.
The second scene demonstrates strokes with overlapping square caps
(these strokes are currently expressed as rects painted with the NonZero
fill rule).
