Don't use analytic clip FPs when drawing to stencil

It doesn't make sense to multiply by coverage when drawing to stencil.
This could theoretically work with FPs that discard and/or modify
the sample mask, but for the time being an analytic FP means one that
calculates a coverage value.

Bug: skia:7190
Change-Id: I44140a5823f8683ec08244bdf9d369f51fa05dd9
Reviewed-on: https://skia-review.googlesource.com/68362
Reviewed-by: Brian Salomon <bsalomon@google.com>
Commit-Queue: Chris Dalton <csmartdalton@google.com>
13 files changed