Split GrConstColorProcessor into three separate .fp effects.

ConstColorProcessor contained three separate InputModes with their own
unique behaviors, but every (non-test) call site simply hardcoded one of
the InputModes.

This change also allows the actual const-color processor to remove the
inputFP entirely; it is never sampled.

The GM slide has been split into three separate slides as well.

Change-Id: I2b77f4eab4d655f06e3704fb6fde8d4f8c70a075
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/301987
Commit-Queue: John Stiles <johnstiles@google.com>
Reviewed-by: Brian Salomon <bsalomon@google.com>
24 files changed