Admin menu: current item should have an aria-haspopup attribute when folded

[afercia]

See related: #32346

When the admin menu is folded or auto-folded (but not when in responsive view) the current menu item should have an aria-haspopup="true" attribute like all the other menu items since it does have a fly-out sub-menu.
Should probably be set and removed with JavaScript depending on the menu collapsed/expanded status.

With the attribute set, screen readers would correctly announce the menu item has a sub-menu, see screenshot below:

Reference:
​http://www.w3.org/TR/wai-aria/states_and_properties#aria-haspopup
aria-haspopup (property)
Indicates that the element has a popup context menu or sub-level menu.

[afercia]

First pass. Tries to detect when the menu is folded or auto-folded. Since the auto-fold CSS class on the body doesn't get removed in some cases, tries to detect when window.innerWidth is in the range > 782 and <= 960. Would greatly appreciate some leads/committers JavaScript feedback.

[afercia]

To recap:

• currently, when the admin menu is expanded, the menu items with sub-items have an aria-haspopup=true attribute except the current active menu item which is displayed open and that's correct
• by the way, when the admin menu is collapsed, also the current active menu item (with sub-items) should have an aria-haspopup=true attribute

[afercia]

Refreshed patch.

[afercia]

Assigning to @wonderboymusic as per Slack conversation (see above).

[wonderboymusic]

In 35313:

Administration: the current admin menu item should have an aria-haspopup attribute when the menu is folded.

Unify the jQuery selector caching for window, document, and body.

Props afercia.
Fixes #32578.