constants/performance_level library

1. droid_dex_flutter package
2. documentation
3. constants/performance_level.dart

droid_dex_flutter package

1. Libraries
2. constants/performance_class
3. constants/performance_class_weight_pair
4. constants/performance_level
5. droid_dex_flutter
6. droid_dex_flutter_method_channel
7. droid_dex_flutter_platform_interface