The MenuView component would happily re-render itself when the list of

menu items changed, but the menu items themselves didn't reflect changes

to the MenuItem attributes. This means that if a label or icon

changed, the menu would have to be explicitly re-rendered to reflect it,

and that operation could be relatively heavy.
Now, attributes will re-render part of or the entirety of the specific

menu item that changed.
To faciliate this, the code for building menu items has changed to

instantiate views specific to each menu item type. This lets us contain

the render logic, DOM updating, and event handling in individual views,

simplifying both those code paths and MenuView itself.
This work also made clear that we had some state management issues. We

weren't unregistering keyboard shortcuts when the menu items were

replaced, causing warnings. We're now able to make use of the full

BaseView.remove() logic to tear down each menu item properly when

replacing menu items or tearing down a MenuView.
One additional but related change is that the onClick() handlers for

menu items now take a MenuItem parameter as the first parameter,

giving handlers the ability to easily manipulate or access state on the

appropriate menu item.

Unit tests pass.
Tested that I could dynamically change state on menu items and that

they re-rendered correctly.