Wayland: Improve support for discrete scrolling

This adds support for high-resolution scroll input scaled to match
legacy discrete scroll input.  It is available on compositors that
support wl_seat version 8 or later.

High-resolution "discrete" values now replace non-scaled scroll
values when available.

src/wl_init.c

@@ -135,7 +135,7 @@ static void registryHandleGlobal(void* userData,
         {
             _glfw.wl.seat =
                 wl_registry_bind(registry, name, &wl_seat_interface,
-                                 _glfw_min(5, version));
+                                 _glfw_min(8, version));
             _glfwAddSeatListenerWayland(_glfw.wl.seat);
         }
     }