split SkPaint into separate impl files

Bug: skia:
Change-Id: If82d39be1f85f9c9487e232b56c72dde175243ab
Reviewed-on: https://skia-review.googlesource.com/c/160022
Reviewed-by: Herb Derby <herb@google.com>
Commit-Queue: Mike Reed <reed@google.com>
3 files changed