Option to expand admin menu with click instead of hover

[sjnbham]

Change the behavior of admin menu top-level links. Have them expand on click instead of on hover events. This will improve accessibility:

​https://www.liquidlight.co.uk/blog/navigation-drop-downs-should-they-be-hover-or-click/

It would also address another issue:

https://core.trac.wordpress.org/ticket/48471#comment:6

If there are concerns about preference, this could be an option instead of removing the ability to hover entirely, but onclick could be the default.

[sabernhardt]

The current plan on #48894 is to make all of the toolbar's dropdowns expand on click (when JavaScript is enabled).

@sjnbham If you want to add to the discussion on #48894, please comment there.

This ticket probably could be closed as a duplicate of the other, if the direction on that ticket stays the same.

[sjnbham]

Duplicate of #48894.

Closing as duplicate of https://core.trac.wordpress.org/ticket/48894