Add dialog role tests to HTML-AAM. This should be in a separate file because the inert status of the dialog would throw off the other tests in [roles.html](https://github.com/web-platform-tests/wpt/blob/master/html-aam/roles.html). And add a comment pointer ([alphabetically after `dfn`](https://github.com/web-platform-tests/wpt/blob/master/html-aam/roles.html#L54)) from roles.html to the new file.
Add dialog role tests to HTML-AAM.
This should be in a separate file because the inert status of the dialog would throw off the other tests in roles.html.
And add a comment pointer (alphabetically after
dfn) from roles.html to the new file.