Improved synchronization of the audio with the display of letters

[PrimCarol]

Improved sound playback for each letter, now the sound plays once a letter has been displayed. Before, the sound was played at the beginning of the interpretation of each letter, regardless of how long it took to be displayed, being out of sync with the audio and the display of the letter.

...
// To save the letters already displayed. 
List<int> charactersShowed = new List<int>();
...

public IEnumerator AnimateTextIn(List<DialogueCommand> commands, string processedMessage, AudioClip voice_sound, Action onFinish){
    ...
    // When the letter reaches its maximum size, it is saved as already displayed, and then the sound is played.
    if (charSize == 1 && !charactersShowed.Contains(j)){
        PlayDialogueSound(voice_sound);
        charactersShowed.Add(j);
    }
    ...
}

And a small sanity check in case you don't want or forget to put an audio.

private void PlayDialogueSound(AudioClip voice_sound){
    // Sanity Check
    if (audioSourceGroup == null || voice_sound == null) { return; }
    ...
}