Exception for changing channelCount on ScriptProcessorNode does not match browsers

[bzbarsky]

https://webaudio.github.io/web-audio-api/#dom-audionode-channelcount says:

ScriptProcessorNode
The channel count cannot be changed, and an InvalidStateError exception
MUST be thrown for any attempt to change the value.

Testcase:

var ctx = new AudioContext
var n = ctx.createScriptProcessor(2048, 3)
try { n.channelCount = 2  } catch (e) { console.log(e.name) }

logs "NotSupportedError" in both Chrome and Firefox.

[padenot]

Telconf decision: align this node on all the others, and make it throw "NotSupportedError", which makes more sense.