Roll Flutter Engine from 78c63d3c2c68 to 9869d47a2736 (1 revision) (#142842)

https://github.com/flutter/engine/compare/78c63d3c2c68...9869d47a2736

2024-02-02 chinmaygarde@google.com [Impeller] Allow playgrounds to use SwiftShader via a flag. (flutter/engine#50298)

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 matanl@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://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

bin/internal/engine.version

-78c63d3c2c68b57e6343e756aa16c0ae963686e1
+9869d47a2736e75470985949137241c48457bf50