This PR doesn't change any logic, it just cleans up some naming and
style in the windows platform layer.

* Rename `WindowsWindowStatePtr` to `WindowsWindowInner`, since it isn't
a pointer type.
* Move window event handler methods into an impl on this type, so that
all of the `state_ptr: &Rc<WindowsWindowInner>` parameters can just be
replaced with `&self`.
* In window creation, use a `match` instead of a conditional followed by
an unwrap

There's a lot of whitespace in the diff, so view it with `w=1`.

Release Notes:

- N/A