Rename SkInsetConvexPolygon to SkOffsetPolygon.

Prep for adding new offset routines.

Change-Id: I261c22d9998e5ae4567b697c5f20a31f20777ac1
Reviewed-on: https://skia-review.googlesource.com/116800
Reviewed-by: Robert Phillips <robertphillips@google.com>
Commit-Queue: Jim Van Verth <jvanverth@google.com>
6 files changed