Roll Flutter Engine from 8c521eb24171 to 6a3b0216ff5b (4 revisions) (#143251)

https://github.com/flutter/engine/compare/8c521eb24171...6a3b0216ff5b

2024-02-09 30870216+gaaclarke@users.noreply.github.com [Impeller] cleaned up StrokePathGeometry and removed runtime polymorphism (flutter/engine#50506)
2024-02-09 ditman@gmail.com [web] Fix HtmlViewEmbedder.dispose (flutter/engine#50482)
2024-02-09 skia-flutter-autoroll@skia.org Roll Dart SDK from 03130d49f214 to 444f7a422da4 (6 revisions) (flutter/engine#50502)
2024-02-09 jonahwilliams@google.com [Impeller] improve performance of polyline and stroke generation by reducing allocation and lambda usage. (flutter/engine#50379)

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

-8c521eb24171351413d4a2a0a21e32e113b90b11
+6a3b0216ff5b85acdd3309f36df9440993f3f6a8

dev/integration_tests/release_smoke_test/lib/main.dart

@@ -15,7 +15,7 @@ Future<void> main() async {
   print(text.toDiagnosticsNode());
   print(text.toStringDeep());
   // regression test for https://github.com/flutter/flutter/issues/49601
-  final List<int> computed = await compute(_utf8Encode, 'test', debugLabel: null);
+  final List<int> computed = await compute(_utf8Encode, 'test');
   print(computed);
   runApp(
     const Center(