feat(notification): add EmbedderMsg::ShowNotification (#36055)

Signed-off-by: Jason Tsai <git@pews.dev>

components/constellation/tracing.rs

@@ -235,6 +235,7 @@ mod from_script {
                 Self::PlayGamepadHapticEffect(..) => target_variant!("PlayGamepadHapticEffect"),
                 Self::StopGamepadHapticEffect(..) => target_variant!("StopGamepadHapticEffect"),
                 Self::ShutdownComplete => target_variant!("ShutdownComplete"),
+                Self::ShowNotification(..) => target_variant!("ShowNotification"),
             }
         }
     }