Add aria-haspopup to trigger element and missing role/tabindex for menu items.
Additionally, change old role="presentation" for dividers to role="separator".
Fixes #15829 (closed)
Note that there are still outstanding issues with the current ARIA-fication of menus (particularly with their JS-based behavior). This fix only introduces the correct (required, in the case of role="menuitem and role="presentation" on the <li> elements) role assignments.
/cc @mdo @cvrebert