Finish safe area implementation

https://github.com/rust-windowing/winit/pull/3890 introduced Window::safe_area, but the implementation isn't completed on all platforms. Tracking this here:

• Android: https://github.com/rust-windowing/winit/pull/4506
• AppKit / macOS: Implemented
• Orbital
• UIKit / iOS: Implemented
• Wayland: No protocol for that at the time of writing.
• Web: Calculate independently of scroll position, https://github.com/rust-windowing/winit/pull/3890#issuecomment-2438243038
• Windows
• X11
• Figure out the semantics wrt. soft keyboards: https://github.com/rust-windowing/winit/pull/4528

Maintainers: Feel free to check the box and remove the corresponding label, either if the implementation is completed, or it doesn't apply to that platform.

Note: Make sure to also wire it up so that RedrawRequested events are emitted when the safe area / insets change.

See also https://github.com/rust-windowing/winit/issues/3911.

Do not close this issue before the ## Platform-specific section on safe_area is updated too.

Start by reviewing the safe_area implementation introduced in PR 3890 and the linked platform work, including Android PR 4506 and the Web discussion. Check each remaining platform item and the soft-keyboard semantics, and ensure RedrawRequested is emitted when insets change. Done means applicable checklist items are resolved and the Platform-specific section documents safe_area.