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/compositing/tracing.rs

@@ -51,8 +51,6 @@ mod from_constellation {
                 Self::AddSystemFont(..) => target!("AddSystemFont"),
                 Self::AddFontInstance(..) => target!("AddFontInstance"),
                 Self::RemoveFonts(..) => target!("RemoveFonts"),
-                Self::GetScreenSize(..) => target!("GetScreenSize"),
-                Self::GetAvailableScreenSize(..) => target!("GetAvailableScreenSize"),
                 Self::CollectMemoryReport(..) => target!("CollectMemoryReport"),
                 Self::Viewport(..) => target!("Viewport"),
                 Self::GenerateImageKeysForPipeline(..) => target!("GenerateImageKeysForPipeline"),