Roll Flutter Engine from a7c785884903 to 3e8b0deffe4e (1 revision) (#144629)

https://github.com/flutter/engine/compare/a7c785884903...3e8b0deffe4e

2024-03-05 zanderso@users.noreply.github.com Folds concurrent job calculation into `tools/gn` (flutter/engine#51193)

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 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

-a7c785884903d6df32d37d755428c88e755e205e
+3e8b0deffe4e01fa7364024a0f0f2fda01909a9f