Roll Flutter Engine from 8389ad914b21 to a98348946d61 (4 revisions) (#134487)

https://github.com/flutter/engine/compare/8389ad914b21...a98348946d61

2023-09-12 jason-simmons@users.noreply.github.com Roll libwebp to 1.3.1 (flutter/engine#45675)
2023-09-11 skia-flutter-autoroll@skia.org Roll Skia from 0b8d2203ab35 to c4e94d5febdc (5 revisions) (flutter/engine#45679)
2023-09-11 chinmaygarde@google.com Pipe VMA asserts to FML. (flutter/engine#45661)
2023-09-11 skia-flutter-autoroll@skia.org Roll Skia from e6225224fb4e to 0b8d2203ab35 (9 revisions) (flutter/engine#45671)

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://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

-8389ad914b21af99999c432fd04ba4c84d95e2fc
+a98348946d615380f20e9b3130da6fc9cf214af3