Aria-description doesn't work

[calebeby]

Hi, it looks like aria-description isn't looked at for the computeAccessibleDescription computation. I'm not sure why the aria-description attribute isn't mentioned in the spec here, but it is described here: https://w3c.github.io/aria/#aria-description.

It feels like something that should be factored in even though the accname spec doesn't mention it

[eps1lon]

I guess we can do this in anticipation of w3c/accname#68