[sksg] Add 'plane' geometry node

SG geometry corresponding to SkCanvas::drawPaint().

TBR=

Change-Id: I3b368adda187fb92f524756496a3694c03a3113d
Reviewed-on: https://skia-review.googlesource.com/108562
Reviewed-by: Florin Malita <fmalita@chromium.org>
Commit-Queue: Florin Malita <fmalita@chromium.org>
4 files changed