Lift atlas clip FP creation out of GrClip::apply

Atlas clips always had a potential point of failure: If the SDC's
opsTask ever got closed between GrClip::apply and
GrOpsTask::addDrawOp, their mask would have gotten sent to the wrong
opsTask. It didn't _look_ like this could happen with the current
code, but it could have also been inadvertently changed quite easily.

This CL adds a "pathsForClipAtlas" array for GrClip::apply to fill out
instead of creating FPs. The SDC then generates the actual clip atlas
FPs once it knows exactly which opsTask they will belong in.

Bug: chromium:928984
Change-Id: I507ab13b2b5e8c3c3c1916d97611297dbbd8a522
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/389926
Commit-Queue: Chris Dalton <csmartdalton@google.com>
Reviewed-by: Michael Ludwig <michaelludwig@google.com>
14 files changed