Audio service for Android (#39)

[AlmasB]

No description provided.

[jperedadnr]

A DummyAudioService class is required, so API jar does include the impl package.

[AlmasB]

I've resolved remaining comments and extracted them here for clarity:

1. I will add AUDIO to client plugin, once this is merged.
2. setOnFinished() is now gone. Path API is used on JDK11 side.

As for media status, I think we still come back to the same issue of not having enough info. For example, when looping is false, PLAY will eventually internally change to STOP. Since there are no listeners, the state, from our perspective, is still PLAY and not STOP. We can't readily monitor this change with Sound. Perhaps, instead we should think about possible uses cases and then go from there?

I propose we don't add any status related API in the first version on the basis that we can't reliably obtain that information for both music and audio. After the first version is released, the community feedback and use cases should help guide the public API, which will bring us much closer to the desired API than if we were to consider it only theoretically.

4. I propose we keep the synchronous mediaPlayer.prepare(). This means the following sequence of calls should always succeed:

Optional<Audio> audio = service.loadAudio(...);
audio.ifPresent(a -> a.play());

If the user wants to load the audio from a background thread, they can, for example, by using Thread directly, or javafx Task<>. So, just let the user have the control over the flow. Making load asynchronous means we have to also provide some kind of a status listener, adding extra steps to the call site.

After these are resolved, I'll start finalizing the PR.

[jperedadnr]

I'm okay with your proposal. Audio status could be added later on if needed.

[AlmasB]

This PR is now ready for a full review and then merge. Sample test video is available for Android 10, showing use of public API and working functionality for both music and sound.

[johanvos]

In the longer term, it would be good if we can have this for iOS and Android in OpenJFX, as an implementation for the OpenJFX API's.
For now, Attach is a good place to test and experiment.

[jperedadnr]

@AlmasB Already filed this for you: gluonhq/gluonfx-maven-plugin#241