webdriver: Synchronize "close window" command & Return correct error type (#38620)

1. Synchronize [Close
Window](https://w3c.github.io/webdriver/#dfn-close-window) command to
reduce intermittency
2. There was a update last month exposing that we are not returning
correct error type for Session getter.
https://github.com/web-platform-tests/wpt/pull/53735
3. Other trivial fix

Testing: 
- `/webdriver/tests/classic/close_window/close.py` can now fully pass.
- `/webdriver/tests/classic/delete_session/*` can now fully pass.

---------

Signed-off-by: Euclid Ye <euclid.ye@huawei.com>

components/shared/embedder/webdriver.rs

@@ -151,7 +151,7 @@ pub enum WebDriverCommandMsg {
     /// associated with the new webview, and sets a "load status sender" if provided.
     NewWebView(IpcSender<WebViewId>, Option<IpcSender<WebDriverLoadStatus>>),
     /// Close the webview associated with the provided id.
-    CloseWebView(WebViewId),
+    CloseWebView(WebViewId, IpcSender<()>),
     /// Focus the webview associated with the provided id.
     /// Sends back a bool indicating whether the focus was successfully set.
     FocusWebView(WebViewId, IpcSender<bool>),