Add UIA support for menus

[mwcampbell]

This encompasses both menu bars and popup/context menus. These implement keyboard focus and selection much like list boxes. But menus have their own quirky events, and we'll need to make sure our implementation of these events works correctly with all of the Windows screen readers.

[mwcampbell]

I forgot a couple more patterns we'll need for these controls:

Menu items will need to conditionally implement the expand/collapse pattern, since some menu items are submenus.

Menu items will also need to conditionally implement the toggle pattern, since some can be checked like check boxes.