Roll Flutter Engine from 090754879679 to 21437d384b56 (1 revision) (#133072)

https://github.com/flutter/engine/compare/090754879679...21437d384b56

2023-08-22 30870216+gaaclarke@users.noreply.github.com [Impeller] Tiny optimizations for text rendering (avoiding extra ops and copies). (flutter/engine#44822)

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 jimgraham@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

-0907548796799da484cb4c365fb34597fd44e208
+21437d384b565dc3d4f0f3a12633bac6a14b0888