Need to handle DetachArrayBuffer throwing

[bzbarsky]

See discussion in whatwg/html#4601 -- DetachArrayBuffer can throw if the ArrayBuffer is not detachable.

WebAudio kinda-implicitly invokes DetachArrayBuffer via a link hidden in https://webaudio.github.io/web-audio-api/#acquire-the-content and similarly in https://webaudio.github.io/web-audio-api/#dom-baseaudiocontext-decodeaudiodata

Ideally, the control flow and the fact that exceptions can get thrown here would be made clear, and there would be web platform tests for this. Worth checking what browsers actually do.

[bzbarsky]

Oh, this was already filed as #1861