Use current variation position in cloning typeface.

The FreeType and CoreText ports would use the default value for an axis
instead of the current value for any unspecified axes. Change this so
that when cloning a typeface any unspecified axes preferentially use the
current axis value if it is known.

Also adds a test that unspecified axes are not changed when cloning.

Change-Id: I751ee5517f1d6b827c6d4ab245e9d681c8df6b42
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/370456
Reviewed-by: Herb Derby <herb@google.com>
Reviewed-by: Dominik Röttsches <drott@chromium.org>
Commit-Queue: Ben Wagner <bungeman@google.com>
5 files changed