Fix AudioContext not being properly resumed on iOS 15. (#4062)
Fix AudioContext not being properly resumed on iOS 15. (#4062)

* Fix AudioContext not being properly resumed on iOS 15.

* Add null check to AudioContext and fix comments.

* Add null check to onstatechange callback.

* Improve handling of errors around auto-play when resuming the AudioContext.

* Add further checks for Auto-Play.

* Safely remove all listeners on destroy and use constants.

* Initialize the _attached variables in constructor.

* Use constant for 'running'.
MicroWorldwide/PlayCanvas,playcanvas/engine,playcanvas/engine,MicroWorldwide/PlayCanvas