Extract headphone key listener to `HeadphoneKeyEventWired`

Move the DDHidLib headphone button event listener from `HeadphoneKey` to
`HeadphoneKeyEventWired`. This creates a common interface for both wired
and wireless Bluetooth headphones.

The DDHidLib listener now lives in its own class dedicated to wired
headphones. A new `HeadphoneKeyEventBluetooth` will set up the event
listener for Bluetooth headphones.

Both `HeadphoneKeyEvent_` listeners call a delegate method set up on
`HeadphoneKey` that relays the pressed headphone button.

0 files changed, 0 insertions, 0 deletions