Add SkTypefaceProxy serialization

Introduce SkTypefaceProxyPrototype that represents the
serialized form of SkTypefaceProxy. Add a basic test to
make sure it all works.

Move SkTypefaceProxy ctor implementation to .cpp.

Bug: skia:14163
Change-Id: I715b5042b2f308c9c9ef557caa94ea9fc749f8f9
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/654543
Reviewed-by: Ben Wagner <bungeman@google.com>
Commit-Queue: Herb Derby <herb@google.com>
6 files changed