Simplify the boilerplate of cloning a fragment processor.

GrFragmentProcessor now provides an (explicit) copy constructor which
clones all child processors and flags from the passed-in FP. Since we no
longer have flags which propagate up to the root node of the FP tree,
all flags are now safe to copy, since a cloned FP also clones all of its
children.

Change-Id: Ia9f80e0ec540ed1056d25dbb1861a174a1d55f4b
Bug: skia:12299
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/437836
Commit-Queue: John Stiles <johnstiles@google.com>
Commit-Queue: Brian Salomon <bsalomon@google.com>
Auto-Submit: John Stiles <johnstiles@google.com>
Reviewed-by: Brian Salomon <bsalomon@google.com>
20 files changed