Update: option element mapping table

[scottaohara]

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)

related to https://github.com/whatwg/html/pull/10586 (among other customizable select prs/issues)

Test, Documentation and Implementation tracking

Once this PR has been reviewed and has consensus from the working group, tests should be written and issues should be opened on browsers. Add N/A and check when not applicable.

• [ ] "author MUST" tests:
• [ ] "user agent MUST" tests:
• [ ] Browser implementations (link to issue or commit):
  • WebKit:
  • Gecko:
  • Blink:
• [ ] Does this need AT implementations?
• [ ] Related APG Issue/PR:
• [ ] MDN Issue/PR: