The ruby rb and rtc sub elements should be added

[frivoal]

In addition to the existing ruby and its rt and rp sub elements, the HTML Ruby Markup Extensions is (re)introducing (by unobsoleting) the rb and rtc elements. (See the introduction and appendix B for rationale.) They should be added (back) to HTML-Aria.

Relevant links to define the elements are: https://www.w3.org/TR/html-ruby-extensions/#the-rb-element and https://www.w3.org/TR/html-ruby-extensions/#the-rtc-element, respectively.

In both cases, I believe the entries for Implicit ARIA semantics (explicitly assigning these in markup is NOT RECOMMENDED) and for ARIA role, state and property allowances should be the same as for rt.

This blocks w3c/html-ruby#45