Use enhanced enums to clarify the image detection code.

Part of a refactor towards flutter/flutter#151911

[C++, Objective-C, Java style guides]: https://github.com/flutter/engine/blob/main/CONTRIBUTING.md#style

https://dart.googlesource.com/sdk.git/+log/e16dc217b1ac..68e559110999

2024-07-30 [email protected] Version 3.6.0-96.0.dev

If this roll has caused a breakage, revert this CL and stop the roller
using the controls here:
https://autoroll.skia.org/r/dart-sdk-flutter-engine
Please CC [email protected],[email protected] on the revert to ensure that a human
is aware of the problem.

To file a bug in Flutter Engine: 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

In 2021, we did some experiments with ML-guided optimisations in the
engine. Ultimately, these didn't provide much benefit, and much of the
information in the documentation is now out-of-date.

For those who need it, this can always be found in the git history.

[C++, Objective-C, Java style guides]: https://github.com/flutter/engine/blob/main/CONTRIBUTING.md#style

…API 35 emulators (#54235)

Previously this was using a zero EGLConfig handle in tests which use an AndroidContextGLImpeller that creates EGL surfaces.  This apparently worked with older emulators, but the API 35 system image requires a real EGLConfig.

See flutter/flutter#152498