egui-winit: Fix unsafe API of Clipboard::new

[dhardy]

So, window_clipboard is not (very actively) maintained and I had a look around...

• Winit doesn't yet have a Clipboard API
• copypasta is maintained, supports the "primary" clipboard, but makes no attempt to provide a Wayland-X11 abstraction
• arboard is maintained, supports HTML and uncompressed RGBA images, but makes no attempt to provide a Wayland-X11 abstraction
• egui-winit does have this abstraction, but with an unsafe API

smithay_clipboard::Clipboard::new notes:

display must be a valid *mut wl_display pointer, and it must remain valid for as long as Clipboard object is alive.

This change addresses the first point (prevents calling Clipboard::new with an arbitrary pointer).

Addressing the second point with Rust's lifetimes would probably be very frustrating. I haven't tried. Addressing it by marking Clipboard::new and State::new as unsafe would be another approach, but would result in all code within State::new being compiled in unsafe mode, would violate your #[forbid(unsafe)] policy and is probably needlessly onerous (given that observing broken behaviour is unlikely), so I opted merely to add documentation here.

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I ran sh/check but egui-glow fails cargo check --all-features (on X11). Nothing to do with me.

[emilk]

Looks good!

I think it would be good to document in crates/egui-winit/Cargo.toml that the wayland feature is required to get the clipboard working on wayland.

[dhardy]

Without the wayland feature Winit won't support Wayland at all, so I don't think there's any point.

[emilk]

needs cargo fmt

[emilk]

cargo check --locked --all-features --all-targets fails

[dhardy]

Updated. Wasn't expecting you to push to my branch, 😆 .

[emilk]

Thanks!