Remove syn 0.15 from our crate graph (fixes #24421)

This required bumps of:

* gleam
* image
* rust-webvr
* webrender
* webxr

components/layout/display_list/webrender_helpers.rs

@@ -338,5 +338,6 @@ fn build_common_item_properties(
         // TODO(gw): Make use of the WR backface visibility functionality.
         flags: PrimitiveFlags::default(),
         hit_info: tag,
+        item_key: None,
     }
 }