use bit 15 to encode page information in glyph UV

Store the page information in bit 15 of the glyph texture UV.
This code is specifically designed to only use 16-bits of
significand.

Change-Id: I36f268b5b131eaad46b05c67ffd4b7a55cfa2bde
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/313519
Reviewed-by: Chris Dalton <csmartdalton@google.com>
Commit-Queue: Herb Derby <herb@google.com>
2 files changed