Add renderSizeHint handling to AudioContext constructor

[mjwilson-google]

Currently, there is specific text about renderSizeHint in the OfflineAudioContext constructor here: https://webaudio.github.io/web-audio-api/#OfflineAudioContext-constructors

However, text to handle this is missing from the AudioContext constructor here: https://webaudio.github.io/web-audio-api/#AudioContext-constructors

We should add text to AudioContext constructor as well.