interactive: Refactor natural_geometry/tiled state handling

Currently, snapping to a screen edge and then snapping to maximize
results in both the natural_geometry and tiled state of the view
getting messed up. After unmaximize, the view ends up in a weird
state (tiled location but natural/untiled size).

There are also a couple of sketchy things going on in the code:

- interactive_begin() pokes its own values into view->natural_geometry
  to force view_maximize() to set a particular geometry.

- interactive_end() "fixes" view->natural_geometry after calling
  view_maximize() to save the original geometry from the start of the
  interactive move/resize.

To fix all this:

- Adjust/expand the API of view.c so that the interactive.c can
  avoid this "back door" of overwriting view->natural_geometry
  directly.

- Save the natural geometry and the tiled state of the view in
  interactive_begin() when starting to move the view.  When done,
  interactive_end() will update the tiled state if appropriate but
  *not* overwrite the natural geometry.

src/xdg.c

@@ -144,7 +144,8 @@ static void
 handle_request_maximize(struct wl_listener *listener, void *data)
 {
 	struct view *view = wl_container_of(listener, view, request_maximize);
-	view_maximize(view, view->xdg_surface->toplevel->requested.maximized);
+	view_maximize(view, view->xdg_surface->toplevel->requested.maximized,
+		/*store_natural_geometry*/ true);
 }
 
 static void
@@ -310,7 +311,8 @@ xdg_toplevel_view_map(struct view *view)
 			view_set_fullscreen(view, true,
 				requested->fullscreen_output);
 		} else if (!view->maximized && requested->maximized) {
-			view_maximize(view, true);
+			view_maximize(view, true,
+				/*store_natural_geometry*/ true);
 		}
 
 		view_moved(view);