When the split Publish button was converted into the new

rb-c-menu-button component, it exposed a pre-existing problem where

the review draft banner (which is always present on a review request

page) was accepting events.
This wasn't a problem on 3.x, because we got lucky. Previously, on

3.x through 4.0 RC1, the banner was marked as hidden with a .hidden

class, and that enabled a visibility: hidden. This kept anything from

really happening in that banner.
The newer version regressed this due to a CSS rule for

rb-c-menu-button that unconditionally set visibility: visible on the

menu. This, along with some combination of the transform to keep it

off-screen and possibly the position: absolute or some other rule, was

keeping the visible menu off-screen but the events on-screen.
There's two bugs here:
1) rb-c-menu shouldn't have been set to visibility: visible inside

   a menu button, unless the menu was open. This CSS rule has been

   separated from another group of rules to ensure this.
2) The review banner should have been hidden from events entirely. This

   is being handled by setting the hidden attribute, which will hide

   the element and all children, no matter what, from the render tree,

   event tree, and accessibility tree.

Tested all menu buttons in the UI to make sure they worked correctly,

and opened/closed correctly. Made sure they weren't able to receive

events when closed.
Tested that, with the above fix alone, the empty review problem was

gone.
Reverted that fix, and added fix #2, for the review banner's hidden state.

Verified that also solved the problem. Verified the review properly opened

when adding a new comment, and that publish/discard worked.
Tested the combination of both, making sure the issue was still fixed and

that the menu worked when the banner was open.
JavaScript unit tests passed.