Roll Flutter Engine from 647cf405f3dc to 3e661e0a58cc (3 revisions) (#139609)

https://github.com/flutter/engine/compare/647cf405f3dc...3e661e0a58cc

2023-12-05 jason-simmons@users.noreply.github.com [Impeller] Declare specialization constants as floats. (flutter/engine#48644)
2023-12-05 102626803+drewroengoogle@users.noreply.github.com Fix labeler not actually doing any labeling (flutter/engine#48701)
2023-12-05 dnfield@google.com Roll abseil to d07bb1bc8e59b37204d457ee365b52b0d11feec0 (flutter/engine#48700)

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 chinmaygarde@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

-647cf405f3dc3a62ef7abb2dcca08166acdf5200
+3e661e0a58cc0d8f1f993c06febf6f38fe5534fa