Better serialize variations, separate SkFontData.

SkFontDescriptor and its serialization and usage are updated to better
reflect how variations should be serialized. In addition this begins
teasing apart SkFontData since it is now mostly an artifact of how the
FreeType port works than anything else.

This also removes SkTypeface::MakeFromFontData since it is no longer
used and since SkFontData (which it takes as a parameter) was never
public. SkFontMgr::makeFromFontData now only exists to support older
skps and may be removed in the future.

Change-Id: I266bd5e87de85788661cdf5c571592ea1f2ae669
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/307344
Reviewed-by: Mike Reed <reed@google.com>
Commit-Queue: Ben Wagner <bungeman@google.com>
6 files changed