Make all SkGlyph fields private

All the scalers are friends, and can still access the fields, but
clients of SkGlyph can no longer access them.

Change-Id: Idbc26de74ceebeac37fa8fec9277ecf8b870e5e9
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/223801
Reviewed-by: Ben Wagner <bungeman@google.com>
Commit-Queue: Herb Derby <herb@google.com>
7 files changed