Add settings UI for controlling how the extension should affect a top
bar items visibility (whether to try to forcefully hide or show an item
or not affect its visibility at all).
Use the title of the PrefsBoxOrderItemRow (AdwActionRow) for the item
name instead of a label in the prefix. Aside from generally being more
correct, item names now wrap correctly, avoiding the settings window
breaking (being cut off by default to the right with even the close
button not showing, until resizing) with long item names.
Also handle drag events in this function so connecting to "drag-end" in
widgets with "GtkDragSource" and a `globalThis` `ScrollManager` instance
aren't needed.
Add the `PrefsBoxOrderListBox`es to the `PrefsPage` via the
`PrefsPage`es UI file.
Also let the `PrefsBoxOrderListBox`es initialize themselves based on the
given box order.