Re-expose winit features for window servers in Linux

[edwloef]

This makes #1777 user-configurable from the top-level iced crate. In my case, disabling the Wayland features saves me 38 dependencies and 1MB of binary size.

This depends on https://github.com/hecrj/window_clipboard/pull/31 to be useful (or even compile), so it's just a draft for now.