mark SkPathBuilder as SK_API

Bug: skia:9000
Change-Id: I9c557460bc9cfbfa6c0506219452ae149b43546c
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/306950
Reviewed-by: Mike Reed <reed@google.com>
Commit-Queue: Mike Reed <reed@google.com>
1 file changed