Display keyboard shortcuts in right gutter of toolbar menus

The way we need to do this kinda sucks, but meh, could have been worse.
We can't just position the accelerators because we don't know how much
space they take up, and floats just will not stay on one line. Taking
advantage of the flexibility of table layout rules seems to work, but
requires more hacks because other elements are stuffed in here already.

I'm contemplating rewriting both PopupToolGroups' styles (List and Menu)
to just use one big table for the popup contents. That might suck less.

VisualEditor fixes (accelerators were not considered in existing CSS):
* I4dd3c55017e7edc25c7af30b5f4c9e103a475016
* I12226f0a674037f904149cc10893f5c154767bfc

Bug: 71855
Change-Id: I38fa56aabf2e857e070f521a1aa8c2da66c044ba
Merge "Display keyboard shortcuts in right gutter of toolbar menus"