Required states can come from native elements [4e8ab6]

[WilcoFiers]

This came from a comment from @JAWS-test on a review

The following shouldn't fail the Element with role attribute has required states and properties rule. The checked state is present even without the aria-checked attribute, because it is on a native checkbox.

<input type="checkbox" role="menuitemcheckbox">

[Jym77]

Decision:

• we need "implicitly set" and "explicitly set" definitions.
• "required state" rule should accept implicitly set states (i.e., this example is good, there is no author error)
• "allowed states" rule should only flagged explicitly set states (i.e. <input type="checkbox" role="button"> shouldn't be flagged for un-allowed aria-checked since it is not an author error).