winit: maximize/fullscreen event support

[repi]

We would like to be able to query current state and/or have reliable events for maximize/minimize/fullscreen toggles as we persist Window location, size and state to the next session.

• Need to get info about window state (maybe only on Windows)
• PR: Feat/fullscreen getters

[repi]

Closing this as it is a very small issue that is better tarcked in the winit repo and/or in our main code repo, not in this ecosystem repo