Roll Flutter Engine from b06478b70a2f to a0ac66ecaa2b (1 revision) (#141498)

https://github.com/flutter/engine/compare/b06478b70a2f...a0ac66ecaa2b

2024-01-13 30870216+gaaclarke@users.noreply.github.com [Impeller] fixed nested save layer mipmap counts (flutter/engine#49778)

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 bdero@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

-b06478b70a2f619c1438f683b892d2031001806d
+a0ac66ecaa2bc913dcaf65f1c130c3f4e181cd36