Roll Skia from 31406e74142b to 20b3af58d4a5 (2 revisions) (flutter/engine#54866)

https://skia.googlesource.com/skia.git/+log/31406e74142b..20b3af58d4a5

2024-08-29 kjlubick@google.com Add moved mock Ganesh files to ganesh_mock target
2024-08-29 danieldilan@google.com GPU support for 101010x color type (RGB only) and fixed some tests.

If this roll has caused a breakage, revert this CL and stop the roller
using the controls here:
https://autoroll.skia.org/r/skia-flutter-autoroll
Please CC brianosman@google.com,egdaniel@google.com,matanl@google.com,rmistry@google.com on the revert to ensure that a human
is aware of the problem.

To file a bug in Skia: https://bugs.chromium.org/p/skia/issues/entry
To file a bug in Flutter: https://github.com/flutter/flutter/issues/new/choose

To report a problem with the AutoRoller itself, please file a bug:
https://issues.skia.org/issues/new?component=1389291&template=1850622

Documentation for the AutoRoller is here:
https://skia.googlesource.com/buildbot/+doc/main/autoroll/README.md

DEPS

@@ -14,7 +14,7 @@ vars = {
   'flutter_git': 'https://flutter.googlesource.com',
   'skia_git': 'https://skia.googlesource.com',
   'llvm_git': 'https://llvm.googlesource.com',
-  'skia_revision': '31406e74142b11759817de0580f7127a2c56c1c3',
+  'skia_revision': '20b3af58d4a5566530e50345533fa524619e2962',
 
   # WARNING: DO NOT EDIT canvaskit_cipd_instance MANUALLY
   # See `lib/web_ui/README.md` for how to roll CanvasKit to a new version.

engine/src/flutter/ci/licenses_golden/licenses_skia

@@ -1,4 +1,4 @@
-Signature: 45a3b5b5c316e276ac245026a51f8b1d
+Signature: fc8d8eb480767ca3ec10c4de6ee905d3
 
 ====================================================================================================
 LIBRARY: etc1