Roll Flutter Engine from 3e66ffa6aae6 to a4b1ef79596a (1 revision) (#135206)

https://github.com/flutter/engine/compare/3e66ffa6aae6...a4b1ef79596a

2023-09-21 skia-flutter-autoroll@skia.org Roll Skia from 81b9c7fd19b2 to c20aeee90da9 (3 revisions) (flutter/engine#46134)

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

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://bugs.chromium.org/p/skia/issues/entry?template=Autoroller+Bug

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

bin/internal/engine.version

-3e66ffa6aae64384a6f4b0fac7da4ff565c00c17
+a4b1ef79596acf36fb707e9a9029237e47074bb8