[graphite] Fill in shader and vertex buffer for DirectMask subruns.

Doesn't handle the transformed case, for the moment.

Bug: skia:13118
Change-Id: I8f792713b224f2b153903f1e65cbb1707e36ca31
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/554343
Reviewed-by: Michael Ludwig <michaelludwig@google.com>
Reviewed-by: Robert Phillips <robertphillips@google.com>
Commit-Queue: Jim Van Verth <jvanverth@google.com>
7 files changed