updateAccessibilityState

Re-reads what VoiceOver should say about the player and sets it as this view's value.

This view calls it when the player is assigned, and while it is in a window, each time the player's status or duration changes. It does not follow the position, because a value that changed on every tick would make VoiceOver speak continuously. So the position read out is the one from the last change. An application that wants a fresh position, for example after a seek, calls this beside its own controls.