Convert GrDitherEffect to a runtime FP

Includes a change so that we can create non-ES2 runtime effects, even
outside of tests/tools. It's still locked to a private API, so clients
can't access the functionality.

Change-Id: Ie0643da2071bd223fccf05b35f3a7b6f7bbc4876
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/423578
Reviewed-by: Brian Salomon <bsalomon@google.com>
Commit-Queue: Brian Osman <brianosman@google.com>
diff --git a/src/gpu/GrProcessorUnitTest.cpp b/src/gpu/GrProcessorUnitTest.cpp
index b4c673f..1779050 100644
--- a/src/gpu/GrProcessorUnitTest.cpp
+++ b/src/gpu/GrProcessorUnitTest.cpp
@@ -146,7 +146,7 @@
  * we verify the count is as expected.  If a new factory is added, then these numbers must be
  * manually adjusted.
  */
-static constexpr int kFPFactoryCount = 17;
+static constexpr int kFPFactoryCount = 16;
 static constexpr int kGPFactoryCount = 14;
 static constexpr int kXPFactoryCount = 4;