libservo: Add ContextMenuElementInformation to for the context menu API (#40607)

This new data structure allows passing more information when popping up
context menus. It's possible in the future that it will be adapted into
a more generic "hit test result" type API ala WebKit, but for now, this
is probably
enough.

Testing: This change includes new API test assertions.

Signed-off-by: Martin Robinson <mrobinson@igalia.com>

components/script/dom/html/htmlimageelement.rs

@@ -1439,6 +1439,15 @@ impl HTMLImageElement {
         self.current_request.borrow_mut().image = Some(Image::Raster(broken_image_icon));
         self.upcast::<Node>().dirty(NodeDamage::Other);
     }
+
+    /// Get the full URL of the current image of this `<img>` element, returning `None` if the URL
+    /// could not be joined with the `Document` URL.
+    pub(crate) fn full_image_url_for_user_interface(&self) -> Option<ServoUrl> {
+        self.owner_document()
+            .base_url()
+            .join(&self.CurrentSrc())
+            .ok()
+    }
 }
 
 #[derive(JSTraceable, MallocSizeOf)]