Implements a simple first pass for a path renderer that uses the
classic Red Book "stencil then cover" method, and linearizes curves
with GPU tessellation shaders.
The new path renderer is disabled by default, and can only be enabled
in the viewer UI or by passing the "--pr gtess" flag.
Change-Id: Ic9354952e93c8b108577961760b4f0daa82d35aa
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/261715
Reviewed-by: Michael Ludwig <michaelludwig@google.com>
Commit-Queue: Chris Dalton <csmartdalton@google.com>
