window: Make monitor from rect finder helper more clearly named

The function finds a suitable logical monitor given the window
rectangle; this wasn't all that clear from the name
"calculate_main_logical_monitor".

This is in preparation for finding a new logical monitor using things
other than the geometry of the window.

Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/2554>

src/wayland/meta-window-wayland.c

@@ -497,7 +497,7 @@ meta_window_wayland_update_main_monitor (MetaWindow                   *window,
    * needed to avoid jumping back and forth between the new and the old, since
    * changing main monitor may cause the window to be resized so that it no
    * longer have that same new main monitor. */
-  to = meta_window_calculate_main_logical_monitor (window);
+  to = meta_window_find_monitor_from_frame_rect (window);
 
   if (from == to)
     return;