* Pipelines downstream of flatten (draw_leaf, coarse) now extract the
  fill rule using a "draw flags" field. Flatten still writes this to the
  path bounding-box structure, which gets propagated to the draw info
  list, and eventually translates to the fill rule written to the PTCL.

* draw_leaf no longer deals with transforming the linewidth for strokes.
  This was a leftover from the previous architecture and the logic is no
  longer needed.

* bbox_clear used to contain a duplicate PathBbox data structure. It now
  uses the one from shader/shared/bbox.wgsl

This continues the work outlined in #303

Wired up the even-odd fill-rule to the CPU version of coarse.

The CPU version of the coarse stage was missing logic to correctly
handle the even-odd fill rule. This change copies over the existing
logic from the GPU version with some added documentation.

Added more draws to the fill_types test scene where different fills
overlap and blend with each other. This is mostly to validate the
even-odd fill logic in the `coarse` stage.

Moved the per-drawobject tile discard logic near the existing tile
inclusion code in the main loop. This avoids the branch conditionals
that were present in each draw tag case branch.