[api] add more arpeggiator styles

[anokta]

enum class ArpeggiatorStyle : BarelyArpeggiatorStyle {
  kUp = 0,
  kDown = 1,
  // kUpDown = 2,
  // kDownUp = 3,
  // kUpAndDown = 4,
  // kDownAndUp = 5,
  // kPinkyUp = 6,
  // kThumbUp = 7,
  kRandom = 8,
};