Add window events (resized, maximized) and getters

[WilliamVenner]

Is your feature request related to a problem? Please describe.
It's not possible to save the user's preference of window size or maximization.

Describe the solution you'd like
Rust window events that fire when the window is resized or maximized.

Describe alternatives you've considered
I have looked into detecting window maximization via JavaScript but it is impossible.

Currently JavaScript's onresize event is satisfactory to save the user's preferred window size.

Additional context
tauri-winit has a Window::is_maximized function on Windows and macOS:

https://github.com/rust-windowing/winit/blob/dabcb1834d4f2c6761854d911ec17f1f01e3cc10/src/platform_impl/windows/window.rs#L414

https://github.com/rust-windowing/winit/blob/629cd86c7cc674c40c1f20b992bdd13784f357dd/src/platform_impl/macos/window.rs#L747

However, Linux seems to be unimplemented:

https://github.com/rust-windowing/winit/blob/ca9c05368e76f70a06cdc34b864711584e5744c2/src/platform_impl/linux/mod.rs#L382

A PR seems to have implemented it, but it's been sitting around since February. Looks like you guys made the right decision to make your own winit branch!

rust-windowing/winit#1848

[lucasfernog]

Maximized event will be implemented when tao provides it.