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/cursor.c

@@ -848,7 +848,7 @@ cursor_button_release(struct seat *seat, struct wlr_pointer_button_event *event)
 
 	if (server->input_mode != LAB_INPUT_STATE_PASSTHROUGH) {
 		/* Exit interactive move/resize mode */
-		interactive_end(server->grabbed_view);
+		interactive_finish(server->grabbed_view);
 		return;
 	}