Xlib must die

Xlib is the legacy strategy for interacting with the X server. It has since been replaced by libxcb, which is lighter and has fewer soundless holes. x11rb wraps around libxcb and reimplements the protocol parsing logic in safe Rust, further reducing the number of places where unsound logic can occur.

List of places in winit where Xlib still lurks:

• Event handling and IME (fixed in https://github.com/rust-windowing/winit/pull/3122)
• Cursor handling code (could use https://github.com/esposm03/xcursor-rs instead)
• SelectXkbEvents (cc https://github.com/rust-windowing/winit/pull/3087)
• Keymap querying

Discussion questions:

• I want to be able to replace x11-dl with tiny-xlib, is this possible?
• Do we want to add a feature to remove Xlib entirely and just use XCB?
• Going further, do we want to add a feature to remove these two external libraries from our X backend altogether and just use x11rb's pure-Rust backend?
  • Is this also available for Wayland?

Start by reviewing the Xlib locations listed in the issue, especially src/platform_impl/linux/x11/util/keys.rs, cursor handling, and SelectXkbEvents; event handling and IME are already marked fixed. Before changing code, resolve the discussion about x11-dl, tiny-xlib, XCB, and x11rb; done requires an agreed migration scope implemented across the affected X11 backend.