libservo: Integrate context menu into the show_embedder_control API (#40402)

This PR integrates showing context menus into the
`WebViewDelegate::show_embedder_control` API. In addition,
`ContextMenuItem` and `ContextMenuAction` data types are exposed which
abstract away the different components of the context menu. Later
changes will implement this API for servoshell as well as add
element-specific actions such as "Select All" and "Copy Image URL".

Testing: This change adds a WebView API test.

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

components/script/dom/document_event_handler.rs

@@ -9,7 +9,6 @@ use std::mem;
 use std::rc::Rc;
 use std::time::{Duration, Instant};
 
-use base::generic_channel;
 use constellation_traits::{KeyboardScroll, ScriptToConstellationMessage};
 use embedder_traits::{
     Cursor, EditingActionEvent, EmbedderMsg, GamepadEvent as EmbedderGamepadEvent,
@@ -763,15 +762,10 @@ impl DocumentEventHandler {
 
         // Step 4. If result is true, then show the UA context menu
         if result {
-            let (sender, receiver) =
-                generic_channel::channel().expect("Failed to create IPC channel.");
-            self.window.send_to_embedder(EmbedderMsg::ShowContextMenu(
-                self.window.webview_id(),
-                sender,
-                None,
-                vec![],
-            ));
-            let _ = receiver.recv().unwrap();
+            self.window
+                .Document()
+                .embedder_controls()
+                .show_context_menu(hit_test_result);
         };
     }