[WebDriver] Properly report error: "No such window" (#37385)

For WebDriver, return "No Such Window" properly according to spec.

Testing: `./mach test-wpt -r --log-raw "D:\servo test log\all.txt"
.\tests\wpt\tests\webdriver\tests\classic\ --product servodriver`

---------

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

components/shared/embedder/webdriver.rs

@@ -84,6 +84,10 @@ pub enum WebDriverCommandMsg {
     CloseWebView(WebViewId),
     /// Focus the webview associated with the provided id.
     FocusWebView(WebViewId),
+    /// Check whether top-level browsing context is open.
+    IsWebViewOpen(WebViewId, IpcSender<bool>),
+    /// Check whether browsing context is open.
+    IsBrowsingContextOpen(BrowsingContextId, IpcSender<bool>),
 }
 
 #[derive(Debug, Deserialize, Serialize)]