backend/wayland: handle high-res scroll events

Receive high-resolution scroll events from the parent compositor using
a Wayland listiner and emit the appropiate wlr_pointer signal.

backend/wayland/backend.c

@@ -346,8 +346,15 @@ static void registry_global(void *data, struct wl_registry *registry,
 		wl->compositor = wl_registry_bind(registry, name,
 			&wl_compositor_interface, 4);
 	} else if (strcmp(iface, wl_seat_interface.name) == 0) {
+		uint32_t target_version = version;
+		if (version < 5) {
+			target_version = 5;
+		}
+		if (version > 8) {
+			target_version = 8;
+		}
 		struct wl_seat *wl_seat = wl_registry_bind(registry, name,
-			&wl_seat_interface, 5);
+			&wl_seat_interface, target_version);
 		if (!create_wl_seat(wl_seat, wl)) {
 			wl_seat_destroy(wl_seat);
 		}

backend/wayland/pointer.c

@@ -187,6 +187,17 @@ static void pointer_handle_axis_discrete(void *data,
 	pointer->axis_discrete = discrete * WLR_POINTER_AXIS_DISCRETE_STEP;
 }
 
+static void pointer_handle_axis_value120(void *data,
+		struct wl_pointer *wl_pointer, uint32_t axis, int32_t value120) {
+	struct wlr_wl_seat *seat = data;
+	struct wlr_wl_pointer *pointer = seat->active_pointer;
+	if (pointer == NULL) {
+		return;
+	}
+
+	pointer->axis_discrete = value120;
+}
+
 static const struct wl_pointer_listener pointer_listener = {
 	.enter = pointer_handle_enter,
 	.leave = pointer_handle_leave,
@@ -197,6 +208,7 @@ static const struct wl_pointer_listener pointer_listener = {
 	.axis_source = pointer_handle_axis_source,
 	.axis_stop = pointer_handle_axis_stop,
 	.axis_discrete = pointer_handle_axis_discrete,
+	.axis_value120 = pointer_handle_axis_value120,
 };
 
 static void gesture_swipe_begin(void *data,