libservo: Start moving WindowMethods to WebViewDelegate (#36223)

`WindowMethods` is used by the embedding layer to get information from
the embedder. This change moves the functionality for getting screen
size and `WebView` offsets to `WebViewDelegate`.

This is important because `WebView`s might be on different screens or
have different offsets on the screen itself, so it makes sense for this
to be per-`WebView` and not global to the embedder. HiDPI and animation
state functionality will move to the embedder in subsequent changes.

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

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- [x] These changes do not require tests because they just modify the
`WebView` API surface a bit.

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

ports/servoshell/desktop/app_state.rs

@@ -392,6 +392,10 @@ impl ServoDelegate for ServoShellServoDelegate {
 }
 
 impl WebViewDelegate for RunningAppState {
+    fn screen_geometry(&self, _webview: WebView) -> Option<servo::ScreenGeometry> {
+        Some(self.inner().window.screen_geometry())
+    }
+
     fn notify_status_text_changed(&self, _webview: servo::WebView, _status: Option<String>) {
         self.inner_mut().need_update = true;
     }