Always give simple circular rrects a shot at being directly blurred on the GPU

I believe we want to do this but split it out of https://codereview.chromium.org/2201133002/ (Implement GPU occluded blur mask filter) b.c. it has its own perf implications and changes several GMs on its own.

GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2232263002

Review-Url: https://codereview.chromium.org/2232263002
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