Move convexity enum out of public

Also, move first-direction into SkPathRef.h so it can be referenced
by name in SkPath (instead of using uint8_t)

No functional change expected.

Change-Id: Ica4a8357a8156fd9a516118f23599a965b0fdd47
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/313980
Reviewed-by: Mike Reed <reed@google.com>
Commit-Queue: Mike Reed <reed@google.com>
25 files changed