change atlas uv encoding

Move the page encoding to bit 14 of UV from bit 0. It would be nice
to use bit 15, but older versions of the iphone don't handle the bit 15
correctly.

Change-Id: Ia8f1a742dfbc85514f8057fdace0e7954aecc593
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/312640
Reviewed-by: Jim Van Verth <jvanverth@google.com>
Commit-Queue: Herb Derby <herb@google.com>
2 files changed