reduce clip-limit for scan converter to avoid quad-edge overflow

reduce clip-limit for scan converter to avoid quad-edge overflow

For raster drawing, we already have a more conservative guard in SkBitmapDevice,
which "tiles" the drawing on 8K boundaries (the smaller limit needed for antialiasing
scan converters). This change is just needed for non-drawing uses of the scan converter.

Bug: skia:7998
Bug: oss-fuzz:8483
Change-Id: Icfee9ca1ffcf93a2a8a3078d9ee10494fa04a6c7
Reviewed-on: https://skia-review.googlesource.com/129628
Reviewed-by: Cary Clark <caryclark@google.com>
Commit-Queue: Mike Reed <reed@google.com>