[canvaskit] Canvas API for loading fonts

There's the barest hint of a "font manager" here.
Basically, nothing smart to deal with bold or fallbacks.

Maybe one day, we'll expose
SkTypeface* matchStyleCSS3(const SkFontStyle& pattern);

and do smart things for fallbacks, but for now that's not
in the immediate future.

Docs-Preview: https://skia.org/?cl=177067
Bug: skia:
Change-Id: Iaeabcbf5ff4511a01b37c16c983e447c25b0e3e7
Reviewed-on: https://skia-review.googlesource.com/c/177067
Reviewed-by: Ben Wagner <bungeman@google.com>
9 files changed