Do an in-place replacement of SkRandom with Fuzz for FilterFuzz

This feels rather clunky, because we aren't using the full potential of the
fuzzer, but it works, it seems.

BUG=skia:4969
GOLD_TRYBOT_URL= https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&issue=1710183002

Review URL: https://codereview.chromium.org/1710183002
3 files changed