why this file automatically creates itself generated_plugin_registrant.dart
generated_plugin_registrant.dart is an automatically generated file that is required to compile your Flutter project as a web application:
This file generated_plugin_registrant. dart exists only to support the web. It exists if Flutter is web-enabled and there is at least one package that has asked for it.
If you're not using Flutter to create a web application, you could drop the web support with the following command:
flutter config --no-enable-web