Possibility of using `Looper.loop()` from the Dart thread?

Hi!

I'm currently trying out `jnigen` to set up a video player. I decided to use the latest `media3.ExoPlayer` as the player, and was able to generate all of the bindings in Dart, which is awesome.

However, when playing around with `ExoPlayer` I ran into threading issues:

```dart
_player = ExoPlayer_Builder(context).build();
_player.play(); // <- Throws an exception saying that the access happened in a wrong thread
```

I was able to get around this by setting the looper for `ExoPlayer_Builder` to the looper of the Dart's thread (and preparing it beforehand):

```dart
Looper.prepare();

_player = ExoPlayer_Builder(context).setLooper(Looper.myLooper()).build();
_player.play(); // <- All good now
```

However, when adding callback listeners to the player, no callbacks actually go through. This is because the `Looper.loop()` was not called anywhere.

I can't call `.loop()` from any of the methods that can be accessed from the UI, as it would hang the thread. I tried calling it as:

```dart
Looper.prepare();

Future.delayed(Duration.zero, () async {
Looper.loop();
});
```

This does work - all callbacks are sent through, but causes the app to crash when hot-restarting, because of an assertion when calling `Dart_EnterIsolate`.

I also tried calling the `.loop()` method from a different Isolate, but that didn't work, because the other Isolate has a different thread.

Attaching the player to the main looper does work, but the problem there is that I have to wrap all of my calls with `ui.runOnPlatformThread()`, and that the closure there seems to overcapture the context, so it's extremely unwieldy to use :(

Not sure how I can get the looper to work. I'm probably doing something stupid because I'm not very well-versed with JNI or the Android platform in general. Any help or ideas would be appreciated