@spec create_child(list()) :: Supervisor.child_spec()

Ensures existing running Flutter engines are killed. Returns a child_spec() that can be supervised, which starts the flutter app

Arguments: :app_name - This should be the atom name of the application that contains the Flutter app.

            It's expected that the compiled AOT Flutter bundle will be found at `priv/flutter_app`.

:env - A map of additions environment variables to set when launching the Flutter engine.

      `%{binary() => binary()}`

:args - A list of strings of extra command line arguments to pass to the Flutter embedder.

:engine_switches - A list of strings of extra command line arguments to pass to the Flutter engine.

              e.g. `"observatory-port=12345"`. See the Flutter embedder documentation for

:bundle_path - A string that's a path to an AOT Flutter bundle. This will override the computed

               path from `:app_name`.

@spec kill() :: :ok

Kills all currently running instances of the flutter engine