[sksg] RenderNode visibility control

Add accessors for enabling/disabling rendering, and remove old-style
OpacityEffect workarounds.

TBR=
Change-Id: I783ada1cb460bce11948f9ca8d6d9d3efa8ca177
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/221896
Reviewed-by: Florin Malita <fmalita@chromium.org>
Commit-Queue: Florin Malita <fmalita@chromium.org>
5 files changed