This PR does a few things:

1. Adds text indicating that UAs should calculate the x of y position of options similar to radio buttons (this is what happens now, but was not specified)
2. Re: the above mentioned x of y (aria-posinset / aria-setsize) for options, the radio button text that this was pulled from had a few wording updates to keep consistency.
3. adds UA MAY to comments of option, indicating what could be done to correct for invalid nesting of interactive elements within options (per upcoming customizable select where this scenario could occur)

this commit also contains commented out content to address w3c/html-aam#568 in a future PR