Stream SkFontMetrics

Write code for streaming SkFontMetrics. Add basic tests.

Bug: skia:14163
Change-Id: I81b2caa5d32c6c905e70dbaf1d96d536ccedbbf8
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/654536
Commit-Queue: Herb Derby <herb@google.com>
Reviewed-by: Robert Phillips <robertphillips@google.com>
7 files changed