Add SkFontMgr implementation for Fuchsia

The new SkFontMgr implementation will be used by Flutter and Chromium on
Fuchsia.

Change-Id: Ibd60a622282556e8557058e92fe865857f7024f9
Reviewed-on: https://skia-review.googlesource.com/c/173800
Reviewed-by: Ben Wagner <bungeman@google.com>
Commit-Queue: Mike Klein <mtklein@google.com>
3 files changed