[svg] Refactor <polygon> and <polyline> to use new parsing

Change-Id: I7cc2dcce4a645326dcacadd28cbe1b3ea5f4ae36
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/367877
Commit-Queue: Tyler Denniston <tdenniston@google.com>
Reviewed-by: Florin Malita <fmalita@chromium.org>
6 files changed