`windows-reactor` window size API improvements

### Suggestion

It would be great to be able to specify an initial x and y position + is_maximized in WindowVisuals

plus, for `on_window_size` to notify is_maximized (it will emit when the maximize button is clicked, however it emits as just a regular size change)

plus, a `on_window_position` to notify of the x and y changes

In my app, I store these properties (along-side width and height) to restore window sizing for the user on app reopen

Start in the windows-reactor implementation around WindowVisuals, on_window_size, and the window event handling entry points. Trace how initial dimensions and resize notifications are represented, then determine where position and maximized state belong. Done means initial x/y and maximized state can be specified, on_window_size reports maximization, and on_window_position reports position changes.

Written by the indexing model from the issue text.