At least indirectly, this is set as object qdata while the
window drag is ongoing, and reset/reconstructed if needed.
Consequently, this edge data does not need to be stored in
the MetaDisplay struct anymore.
Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/2683>
Even though the data is still stored in the display, add a "high
level" meta_window_drag_update_edges() call, so that the cached
edges may be updated while a window drag operation is ongoing.
Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/2683>