Call for review: update "Element with aria-hidden has no focusable content"

Hey everyone,

This PR updates the expectation of the "Element with aria-hidden has no
focusable content" rule, so that test targets cannot be focused through any
mechanism, fixing a couple of issues (
https://github.com/act-rules/act-rules.github.io/issues/643 and
https://github.com/act-rules/act-rules.github.io/issues/1386). Examples
were updated in accordance. Additionally, "focused" and "focusable"
definitions were also updated

https://act-rules.github.io/rules/6cfa84

This PR has a two week period, ending on February 25. If you have comments,
please leave a review before the end of the review period.

Kind regards,
Carlos

PS: it took us 17 months to get here!

-- 
*Carlos Duarte*
LASIGE, Faculdade de Ciências, Universidade de Lisboa
Web: https://www.di.fc.ul.pt/~cad/
Twitter: @carlosapaduarte