Support aria-setsize of -1

[joanmarie]

Steps to reproduce:

1. Load this test case in Chrome (not Firefox):

<div>foo</div>
<ul>
  <li aria-setsize="-1" aria-posinset="5">apples</li>
  <li aria-setsize="-1" aria-posinset="6">bananas</li>
  <li aria-setsize="-1" aria-posinset="7">cantaloupes</li>
</ul>

2. Use JAWS (I have version 2022) to arrow from the div down to the list

Expected results: JAWS would say something to indicate the list size was unknown.

Actual results: JAWS announces that it is a list with 4 items.

According to the ARIA spec:

When specifying aria-setsize, authors MUST set the value to an integer equal to the number of items in the set. If the total number of items is unknown, authors SHOULD set the value of aria-setsize to -1.

Chrome exposes this value to ATs (Firefox doesn't at the moment) and JAWS includes the setsize of -1 in the element information. So I think all that is needed is support in JAWS. However, if JAWS needs something else, please file a bug against Chromium and CC me (jdiggs at igalia dot com).