Extend keyboard support for the SeekBar, and pass unhandled keydown events from components back to the player.
Switch from raw keycodes to the keycode module.
Using `userActions.hotkeys`, which can either be a function to match the hotkeys plugin, or an object with properties like `fullscreenKey`, see the documentation for more info.
This is currently off by default, we will consider turning it on by default in the future, see #5765.
Fixes#4048, fixes#3022.
