Add SkTypeface::getVariationDesignPosition.

Allow users to query a typeface's position in variation design space.

Change-Id: Id7cae439e795b8c9586394f11359fb7fe55e1c0b
Reviewed-on: https://skia-review.googlesource.com/8861
Reviewed-by: Mike Reed <reed@google.com>
Commit-Queue: Ben Wagner <bungeman@google.com>
29 files changed