Enhance Step Sequencer and Song Arranger with Current Arrangement Index

Commit notes

This commit introduces the currentArrangementIndex state to the Step Sequencer and Song Arranger components, allowing for better tracking of the currently active arrangement during playback. The SongArranger component is updated to handle drag-and-drop functionality for pattern management, including the ability to chain patterns and manage repeats. Additionally, the integration of isPlaying and playbackMode props enhances the user experience by visually indicating the currently playing pattern. These changes improve the overall functionality and interactivity of the sequencer.