Pre-crop filled rects to avoid scissor

Pre-crop filled rects to avoid scissor

Updates GrDrawContext to crop filled rects to the clip bounds before
creating batches for them. Also adds clipping logic to ignore scissor
when the draw falls completely inside. These two changes combined
reduce API traffic and improve batching.

In the future this can and should be improved by switching to floating
point clip boundaries, thus allowing us to throw out non pixel aligned
rectangle clips as well.

BUG=skia:
GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2132073002

Review-Url: https://codereview.chromium.org/2132073002