We've had a few places in the UI that implemented their own idea of a

drop-down menu. Each of these looked and worked differently, which can

be fine depending on the use case, but we had very little

standardization around them. They also weren't very accessible to

non-mouse users.
This change introduces a new .rb-c-menu CSS class for defining a menu

and a .rb-c-menu__item class for menu items. It provides some standard

behavior for a menu's defaults, its opened state, and how items are

presented.
It also allows for mixing in some upcoming CSS classes centered around

buttons, for creating a button menu (where each item is just a button).
This class is the first to offer notes on how accessibility should work

and which DOM attributes should be set. The idea is that by including

this as part of the component documentation, we have a basic spec that

dictates how any implementations should behave and what attributes they

should include when using defining the elements. This is something I'm

aiming to do going forward, and should take away a lot of the guess-work

when building implementations.

Made use of this along with some upcoming changes, testing menus and

button menus.
Tested the ARIA tree to ensure that the correct roles and metadata were

set for menus.