Make fragment processor iterators work with range for loops.

When iterating over the coord transforms or texture samplers of a
FP also have access to the owning FP.

Pass a coord transform range to GPs rather than a pointer to an
iterator.

Change-Id: If7c829a67dce6600d7f49e12d6f49f685dcace3a
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/256216
Commit-Queue: Brian Salomon <bsalomon@google.com>
Reviewed-by: Michael Ludwig <michaelludwig@google.com>
46 files changed