Use full precision for QuadEdge attributes on iOS.

We're passing in QuadEdge attributes as half precision, but
kStableLargeNegativeValue is well past any value that can be handled
by half float. Increasing the precision used fixes the issues we're
seeing on iOS 14.

Bug: skia:10594
Change-Id: I650a0930cf8dd9a2369bfeeffc132c0f7f0fa79e
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/342303
Commit-Queue: Jim Van Verth <jvanverth@google.com>
Reviewed-by: Brian Salomon <bsalomon@google.com>
1 file changed