Entries and menubuttons are no longer focusable themselves,
they have focusable children. Since we don't have accessible
objects for those, transfer the focus-related state (focusable
and focused) from the children to the main accessible object.
Rework the way we assign an accessible name to menu buttons,
to make sure we pick up a label, should the button contain
one, and only override the name with "Menu" as a fallback.
The button now claims its menu as a child for a11y purposes,
which makes it possible for ATs to see it when the navigate
the tree top-down.
Update the a11y test to match.
