Persist expanded states for submenus in Twenty Fifteen when customizing menus

[westonruter]

If you have a menu with submenus, and you expand a submenu in Twenty Fifteen, then when you make a change to the menu in the Customizer the partial-refresh will kick in and replace the menu container and lose the expanded states. This is a pain especially if you are trying to customize a nested submenus, as you then have to re-expand the nested submenus with each change to the menus in the Customizer.

[westonruter]

​https://github.com/xwp/wordpress-develop/pull/108

[westonruter]

In 33177.diff​:

• Improve naming of param from wpNavArgs to wpNavMenuArgs for customize-preview-menu-refreshed event params.
• Re-sync expanded states from menu container being replaced
• Prevents main navigation from being re-initialized multiple times when editing a separate menu assigned to Social Links Menu, causing a toggle button to be newly inserted with each social menu change. See duplicated-toggle-buttons.png​.

[westonruter]

In 33491:

Twenty Fifteen: Only re-initialize the main navigation in the Customizer when it is specifically updated.

• Fix a bug where updating the social menu links would cause the main navigation to get its toggle-expanded buttons duplicated.
• Persist any existing submenu expanded states on the updated menu.
• Improve naming of customize-preview-menu-refreshed event param from wpNavArgs to wpNavMenuArgs (old name is retained and marked as deprecated).

Fixes #33177.