Serialize window maximized state in WindowSettings

[landaire]

A user of my Windows application reported a papercut where the application restores its size on next load, but does not restore its maximized state. This PR fixes that.

To test, I patched https://github.com/emilk/eframe_template to use my local code since I knew that template saves/restores window data. Testing methodology was to simply cargo run, maximize the application, then close the application. cargo run again and the application should start maximized.

Closes #1517.

• I have followed the instructions in the PR template
• • This is mostly true, I had difficulties running ./scripts/check.sh for some reason. Possibly a bad Python version?

[emilk]

code LGTM

[github-actions]

Preview available at https://egui-pr-preview.github.io/pr/5554-restorewindowmaximizedstate
Note that it might take a couple seconds for the update to show up after the preview_build workflow has completed.

[landaire]

Just wanted to note I think this fixes #1517 and the last remaining item from #3494. If you can confirm, I can update the PR description to include the magic "closes" text.

[emilk]

Unfortunately, this leads to a deadlock on Mac when running cargo run -p custom_window_frame

See also #3612

[landaire]

Will take a look to see if I can resolve the deadlock.

[landaire]

Left a comment in #3494 and also created rust-windowing/winit#4071.

For now I've removed the erroneous unconditional maximized logic in update_viewport_info. This retains the desired behavior of this diff, while preventing the logic from being invoked on macOS (tested with both cargo run -p custom_window_frame and my original testing steps)