Roll Flutter Engine from 666bc34c61aa to 687f4c761db1 (2 revisions) (#125818)

https://github.com/flutter/engine/compare/666bc34c61aa...687f4c761db1

2023-05-01 skia-flutter-autoroll@skia.org Roll Dart SDK from a433ca08e7e2 to dc4a048e3cf7 (1 revision) (flutter/engine#41636)
2023-05-01 xilaizhang@google.com [flutter roll] Revert "Determine lifecycle by looking at window focus also" (flutter/engine#41626)

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 jsimmons@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

-666bc34c61aab27d98d6a111d92ef278ec9f487f
+687f4c761db18cbed9f02ef0c07ac2c7e9adda42