Keyboard accessibility (arrow keys and enter) in MenuBar

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Arrow-key and enter-key accessibility for MenuBar? with submenus seems to work inconsistently in the master. It works in 1.8 with visualization quirks. There's a bug in 1.9.0a2 (#16784) which prevents the behavior from being observed.

Attached an example based on the Dijit Menus 1.8 demo, but if you just ran that demo off the master this should happen.

To reproduce:

1. Click on any MenuBar? item (mouse or focus+arrow-key+enter).

2. Click on any item of the submenu that opened (mouse or arrow-key+enter). The MenuBar? item is no longer highlit.

3. Click enter. The submenu will re-open but the MenuBar? item won't highlight (you may see a brief flicker of it sort-of-highlighting in the master).

4. Try to use the arrow-keys to traverse the submenu; in 1.8, this works, but in the master, the items won't highlight and clicking enter won't click them (step 5 for what happens on enter click). You can't use escape to close the submenu.

5. Click enter again. In the master, the MenuBar? item will highlight and the submenu will close. (In 1.9.0a2 this is where the bug happens.)

6. Click enter once more. The submenu opens, and you can keyboard traverse its items. If you click a submenu item, the sequencerepeats.

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Example of keyboard accessibility in MenuBar? on master