Adapt AudioTrackList API to new events structure (#15029)
Adapt AudioTrackList API to new events structure (#15029)

This PR adapts the AudioTrackList API to conform to the new events structure.  Part of work for #14578.
mdn/browser-compat-data,mdn/browser-compat-data,chrisdavidmills/browser-compat-data,chrisdavidmills/browser-compat-data