The Collection value menu was a flat list of every collection in the
library, with subcollections set apart by an indent (or hyphens before
606d8f19ba). Build it with Utilities.Internal.createMenuForTarget()
instead, using the new 'filter' feature to limit to collections. The new
FAYT helper preserves matching on subcollections.
If a subcollection is selected, open the path down to the subcollection
when opening the menu. (As of fx153, macOS renders popups as native
menus, which can't be opened to a submenu, so revert to non-native menus
there.) A collection in a submenu can't be a menulist's selected item,
so the condition holds the value and sets the menulist's label and icon
itself, with the collection's path as a tooltip.
c8b841df8a