[native_assets] dart test not adding asset mapping to kernel file

[dcharkes]

ec4e420 caused:

• Removing Flutter dependency causes integration tests to fail google/flutter-mediapipe#33

On a42c38b:

$ ~/dart-sdk/sdk/xcodebuild/ReleaseARM64/dart-sdk/bin/dart --enable-experiment=native-assets test
Resolving dependencies in `/Users/dacoharkes/src/google/flutter-mediapipe/packages/mediapipe-task-text`... 
Downloading packages... 
Got dependencies in `/Users/dacoharkes/src/google/flutter-mediapipe/packages/mediapipe-task-text`.
Building package executable... (2.1s)
Built test:test.
00:00 +2 -2: test/language_detector_executor_test.dart: LanguageDetectorExecutor should run a task [E]                                                                            
  Invalid argument(s): Couldn't resolve native function 'language_detector_create' in 'package:mediapipe_text/src/io/third_party/mediapipe/generated/mediapipe_text_bindings.dart' : No asset with id 'package:mediapipe_text/src/io/third_party/mediapipe/generated/mediapipe_text_bindings.dart' found. Available native assets: . Attempted to fallback to process lookup. dlsym(RTLD_DEFAULT, language_detector_create): symbol not found.
  
  dart:ffi                                                                                      Native._ffi_resolver_function
  package:mediapipe_text/src/io/third_party/mediapipe/generated/mediapipe_text_bindings.dart    language_detector_create
  package:mediapipe_text/src/io/tasks/language_detection/language_detector_executor.dart 35:29  LanguageDetectorExecutor.createWorker
  package:mediapipe_core/src/io/task_executor.dart 56:17                                        TaskExecutor.worker
  package:mediapipe_text/src/io/tasks/language_detection/language_detector_executor.dart 66:7   LanguageDetectorExecutor.detect
  test/language_detector_executor_test.dart 27:54                                               main.<fn>.<fn>

After reverting ec4e420:

$ ~/dart-sdk/sdk/xcodebuild/ReleaseARM64/dart-sdk/bin/dart --enable-experiment=native-assets test
Building package executable... 
Built test:test.
00:00 +4: test/language_detector_executor_test.dart: LanguageDetectorExecutor should run a task                                                                                   INFO: Created TensorFlow Lite XNNPACK delegate for CPU.
WARNING: Attempting to use a delegate that only supports static-sized tensors with a graph that has dynamic-sized tensors (tensor#15 is a dynamic-sized tensor).
WARNING: All log messages before absl::InitializeLog() is called are written to STDERR
W0000 00:00:1715668092.905634 1825992 inference_feedback_manager.cc:114] Feedback manager requires a model with a single signature inference. Disabling support for feedback tensors.
[...]
00:00 +22: All tests passed!                                                                                                                                                      

I can see that the build.dart hook is run, but the mapping is somehow not embedded in the kernel file.

[dcharkes]

Adding P1 for either fix forward or a revert.