Merge #1243

1243: Force-drop the token before calling fire_map_callbacks r=kvark a=kvark

**Connections**
Related to WebGPU update in Gecko

**Description**
Since the token was alive, technically, we saw an assertion firing up about concurrent access to the token root.

**Testing**
Tested in Gecko

Co-authored-by: Dzmitry Malyshau <dmalyshau@mozilla.com>

wgpu-core/src/device/queue.rs

@@ -816,6 +816,8 @@ impl<G: GlobalIdentityHandlerFactory> Global<G> {
             callbacks
         };
 
+        // the map callbacks should execute with nothing locked!
+        drop(token);
         super::fire_map_callbacks(callbacks);
 
         Ok(())