interactive: Refactor natural_geometry/tiled state handling

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.