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>

components/shared/embedder/lib.rs

@@ -636,3 +636,22 @@ pub struct NotificationAction {
     /// Icon's raw image data and metadata.
     pub icon_resource: Option<Arc<Image>>,
 }
+
+/// Information about a `WebView`'s screen geometry and offset. This is used
+/// for the [Screen](https://drafts.csswg.org/cssom-view/#the-screen-interface)
+/// CSSOM APIs and `window.screenLeft` / `window.screenTop`.
+#[derive(Clone, Copy, Debug, Default)]
+pub struct ScreenGeometry {
+    /// The size of the screen in device pixels. This will be converted to
+    /// CSS pixels based on the pixel scaling of the `WebView`.
+    pub size: DeviceIntSize,
+    /// The available size of the screen in device pixels. This size is the size
+    /// available for web content on the screen, and should be `size` minus any system
+    /// toolbars, docks, and interface elements of the browser. This will be converted to
+    /// CSS pixels based on the pixel scaling of the `WebView`.
+    pub available_size: DeviceIntSize,
+    /// The offset of the `WebView` in device pixels for the purposes of the `window.screenLeft`
+    /// and `window.screenTop` APIs. This will be converted to CSS pixels based on the pixel scaling
+    /// of the `WebView`.
+    pub offset: DeviceIntPoint,
+}