Add definition for implicit/explicit ARIA attributes

Add a definition for "ARIA attribute is set", with variations whether it comes from an explicit aria-* attribute, an implicit HTML AAM, or a default value.
Switch "role has all required ARIA attributes" to also apply to implicit roles. These normally have implicitly set attributes (which is why we skipped them initially), and can now be handled by this definition.
Switch "role has all required ARIA attributes" to accept attributes set in any way.
Switch "ARIA attribute permitted" to only look at explicitly set ones. It was more or less already doing that by looking at aria-* HTML attributes, this makes it a bit clearer.

Closes issue(s):

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