Standardize Java unit test location in flutter/plugins #82470
Description
It looks like the standard place for Java unit tests in plugins is android/src/test/, but we have a number that are not:
./packages/google_sign_in/google_sign_in/example/android/app/src/test/java/io/flutter/plugins/googlesignin/GoogleSignInPluginTests.java
./packages/google_maps_flutter/google_maps_flutter/example/android/app/src/test/java/io/flutter/plugins/googlemaps/GoogleMapControllerTest.java
./packages/image_picker/image_picker/example/android/app/src/test/java/io/flutter/plugins/imagepicker/FileUtilTest.java
./packages/image_picker/image_picker/example/android/app/src/test/java/io/flutter/plugins/imagepicker/ImagePickerDelegateTest.java
./packages/image_picker/image_picker/example/android/app/src/test/java/io/flutter/plugins/imagepicker/ImagePickerPluginTest.java
./packages/image_picker/image_picker/example/android/app/src/test/java/io/flutter/plugins/imagepicker/ImageResizerTest.java
./packages/image_picker/image_picker/example/android/app/src/test/java/io/flutter/plugins/imagepicker/ImagePickerCacheTest.java
We should move those to the standard location (and ensure they are run; I'm not sure that unit tests in example/ are actually run by our CI).