Call all ewmh_update_* functions together when necessary

The testcase is changed because it was actually incorrect. Easy to
verify because:
> _NET_CURRENT_DESKTOP
> …
> The index of the current desktop. This is always an integer between 0
> and _NET_NUMBER_OF_DESKTOPS - 1.

Fixes #3696.
Also updates the viewports.

Finally, fixes an issue with _NET_CURRENT_DESKTOP not being updated
after a workspace rename. Example:
- workspaces 1, 2, 3
- rename workspace 1 to 5
- All workspaces changed their index but _NET_CURRENT_DESKTOP was not
updated

src/tree.c

@@ -301,9 +301,7 @@ bool tree_close_internal(Con *con, kill_window_t kill_window, bool dont_kill_par
 
     if (ws == con) {
         DLOG("Closing workspace container %s, updating EWMH atoms\n", ws->name);
-        ewmh_update_number_of_desktops();
-        ewmh_update_desktop_names();
-        ewmh_update_wm_desktop();
+        ewmh_update_desktop_properties();
     }
 
     con_free(con);