Add Drag and Drop in List(box) example

[imhemish]

There are various cases for a drag and drop in list box. It is mostly used for a preference where the user needs to be asked, what should appear first, or what should be applied first in a list of actions. A prime example of this is how search entries in gnome overview should be ranked. There is a drag handle which can be dragged, while an extra menu in suffix of row provides a click option for moving up and down in cases where drag and drop is not available (like a keyboard only system)

some useful links:
https://discourse.gnome.org/t/drag-and-drop-items-in-gtk-listbox-with-gtk-4/9083
https://gitlab.gnome.org/GNOME/gnome-control-center/-/blob/main/panels/search/cc-search-panel.c?ref_type=heads (code where drag and drop functionality in search panel of gnome-control-center is implemented)

[sonnyp]

Checkout the "Drag and Drop" demo.

Discoverability isn't great, we should improve the search.

Also we could split into 2 demos

1. Drag and Drop - with very simply code
2. ListBox with reordering