feat: Allow volume control of Music & Sound with property

[DeathPhoenix22]

Hi,

Issue Link: #1310

Here's an implementation that allow custom Volume configuration of all Sounds & Musics. I've placed the "Master / Global" volume property of the AudioType inside them. This felt pretty natural since the "expert" (GRAPS) of that information is the AudioType itself. This also mean that we could really easily add a new AudioType without much efforts and that new type would automatically mix itself against the Global and the current Audio.

@AlmasB NOTE: I took the initiative to revert the changes made in #1187. Granting access to the internal audio is causing a bug related to volume adjustments in the settings. Whenever a player was adjusting his Global volume, all custom changes made on the audio (getAudio()) was automatically reverted. With this implementation, the conjunction of the 2 values are always kept (via the mix() method)

Example:

Music music = getAssetLoader().loadMusic("rain.mp3");
music.setVolume(0.0);
Timeline timeline = new Timeline(
    new KeyFrame(Duration.seconds(5),
    new KeyValue(music.volumeProperty(), 1.0))
);
FXGL.getAudioPlayer().playMusic(music);
timeline.play();

Note that changing the Global Music volume will also automatically impact all Music:

AudioType.MUSIC.getVolume().set(AudioType.MUSIC.getVolume().get() - 0.1);

I've tested it on my own game and I needed it!
I hope you like it! :)

[DeathPhoenix22]

Automatically handled by the Audio with Property change listeners

[DeathPhoenix22]

No need anymore, the global volumes are automatically mixed with the Media configured sound