[graphite] Consistently ignore path inversion when stroking

This fixes incorrect rendering in the complexclip_aa and related GMs
when rendering with Graphite and disabling MSAA. These GMs have paths
that are sometimes inverted (for fills), but then draws them as
hairlines for visualization.

When MSAA is disabled, the raster atlas strategy would upload a mask
for the regular fill of the stroked outline. It would then apply a
coverage inversion in the shader, causing the hairline borders to
render negated and cover the entire window in transparent blue and
red (blending into a purple over everything).

Since the stroke tessellation ignores inversion (which we could revisit
with a version that adds a stencil test), this forces shapes to
be non-inverted when there is no "fill" in their SkStrokeRec style.

Change-Id: Iee3b59d15d39a1974e1ca2f50062fd4762ba195e
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/1253517
Reviewed-by: Nicolette Prevost <nicolettep@google.com>
Commit-Queue: Michael Ludwig <michaelludwig@google.com>