Review of #1693 found that cast_effects built the picture content that a shadow,
a glow and a reflection are drawn from without converting a tiled fill to
points, so inside a scaled group the reflection of a tiled picture showed
child-space tiles while its face showed the right ones.
The content now goes through paint::tiled_picture_per_point with per_point_xy,
as the face does.
Test: a tiled picture's reflection in groups scaled 0.25, 1600 and 2x0.5 shows
the same colours as in an unscaled group; it fails without the change.
Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>