Roll Flutter Engine from d00e55f7f8ed to a9b87c6288d2 (3 revisions) (#141914)

https://github.com/flutter/engine/compare/d00e55f7f8ed...a9b87c6288d2

2024-01-20 jonahwilliams@google.com [Impeller] null check vertex buffer. (flutter/engine#49915)
2024-01-19 30870216+gaaclarke@users.noreply.github.com [Impeller] adds vulkan golden images (flutter/engine#49849)
2024-01-19 98614782+auto-submit[bot]@users.noreply.github.com Reverts "[Fuchsia] Redo - Use chromium test-scripts to download images and execute tests" (flutter/engine#49908)

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 jonahwilliams@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

-d00e55f7f8ed98d600848cdf8305b956760cf273
+a9b87c6288d2089fe758c3fac2ee056ddc69cbb3