script: Get the screen metrics from the WebViewDelegate instead of via the compositor (#38020)

Similar to #37960, previously, `AvailHeight`, `AvailWidth`, `Height`,
`Width` ask compositor for screen metrics. This PR moves the request to
embedder.

This simplifies code, and reduces workload of compositor, which is
busier most of time.

Testing: No behaviour change. Updated some tests. `Width/Height` matches
other browsers.

---------

Signed-off-by: Euclid Ye <yezhizhenjiakang@gmail.com>

components/constellation/tracing.rs

@@ -215,6 +215,7 @@ mod from_script {
                 Self::NewFavicon(..) => target_variant!("NewFavicon"),
                 Self::HistoryChanged(..) => target_variant!("HistoryChanged"),
                 Self::GetWindowRect(..) => target_variant!("GetWindowRect"),
+                Self::GetScreenMetrics(..) => target_variant!("GetScreenMetrics"),
                 Self::NotifyFullscreenStateChanged(..) => {
                     target_variant!("NotifyFullscreenStateChanged")
                 },