ARIA state or property: various editorial improvements

[WilcoFiers]

This is addressing feedback from the recent ACT TF survey. I've also updated several examples, and filled in a few gaps.

Closes #1849

Need for Call for Review: 1 week, since I'm updating a number of examples

This PR is closely related to #2041, which introduces a new rule that ensures required ID references exist in the page. We're basically splitting that part of this rule off into its own.

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[carlosapaduarte]

From the CG call: remove the exceptions from this rule and create a second rule to address the exceptions (in the first rule include a background note stating the second rule is under development)

[WilcoFiers]

@Jym77 The reason to split this is because that second expectation got unnecessarily complicated. A new rule lets us keep things simple. It also fits better with the requirement to write atomic rules. There are other rules for which we may do things like this too. For example an allowed ARIA attribute is different from a prohibited attribute, from a deprecated attribute.