[ngatoy] Strictly differentiate between painter's order and the sort/draw Zs

Bug: skia:11837
Change-Id: I038aee81e41201668f891df9d589459553b757b2
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/417259
Commit-Queue: Robert Phillips <robertphillips@google.com>
Reviewed-by: Michael Ludwig <michaelludwig@google.com>
6 files changed