include mention of figure/caption

this pr updates `aria-details` to mention `figure` and `figcaption`.

This update is related to HTML AAM's update to the `figure` and `figcaption` elements - w3c/html-aam#359.
It is a follow on to my other PR, #1703 which updates the `caption` role and includes information about `aria-details`.

index.html

@@ -11297,6 +11297,7 @@ <h2>Definitions of States and Properties (all aria-* attributes)</h2>
  <ul>
  <li>Comment: <code>aria-details</code> refers to an element with role <rref>comment</rref>.</li>
  <li>Definition: <code>aria-details</code> is applied to an element with role <rref>term</rref> and refers to an element with role <rref>definition</rref>.</li>
+ <li>Figure: <code>aria-details</code> is applied to an element with role <rref>figure</rref> and refers to an element with role <rref>caption</rref>, or an element witin a <code>caption</code>.</li>
  <li>Footnote: <code>aria-details</code> refers to an element with role <code>doc-footnote</code>. This role is defined in [[DPUB-ARIA-1.0]].</li>
  <li>Endnote: <code>aria-details</code> refers to an element with role <code>doc-endnote</code>. This role is defined in [[DPUB-ARIA-1.0]].</li>
  <li>Description or general annotation: <code>aria-details</code> refers to an element with any other role.</li>