Add wayland-dlopen feature switch

This feature controls whether to load libwayland at runtime using dlopen
instead of linking with it.

Cargo.toml

@@ -16,6 +16,7 @@ rust-version = "1.65.0"
 default = ["x11", "wayland"]
 x11 = ["x11-clipboard"]
 wayland = ["smithay-clipboard"]
+wayland-dlopen = ["smithay-clipboard/dlopen"]
 
 [target.'cfg(windows)'.dependencies]
 clipboard-win = "3.0.2"