Today, both FlutterEngine and InputConnectionAdapter (and via that, FlutterTextUtils) create new FlutterJNI instances.

I'm pretty sure that only FlutterEngine needs one. InputConnectionAdaptor doesn't need any state, it's only using native methods that are stateless.

The only thing that isn't clear to me is whether we'd ever actually need two instances of FlutterJNI - I think there's some case where we'd want that but not today. But we should also make it clearer about when that'd be necessary, which methods care about state, etc.

/cc @xster @jason-simmons