webdriver: Implement the "Get Window Handles" command (#38622)

Implment get window handles according to
[spec](https://w3c.github.io/webdriver/#dfn-window-handles).
- Window handles are supposed to identify `browsing context`. However,
based on `get window handle command` and `get window handles command`,
we only need to care about top level browsing context.
- Back then, we use a random generated uuid for eacch webview id, it is
not correct but still work because all commands depend on `webview id`
and `browsing context id`. The only case we need window handle is is
when webdriver gets window object with js script. Since the object is
converted to the id of window's document node, `get window handle`
should return the same thing.

Action run (with updated expectation):
https://github.com/longvatrong111/servo/actions/runs/16957610535
https://github.com/longvatrong111/servo/actions/runs/16957612027

Some tests may sporadically timeout due to unstable hit test.

cc: @xiaochengh

---------

Signed-off-by: batu_hoang <hoang.binh.trong@huawei.com>

components/shared/embedder/webdriver.rs

@@ -157,6 +157,8 @@ pub enum WebDriverCommandMsg {
     FocusWebView(WebViewId, IpcSender<bool>),
     /// Get focused webview. For now, this is only used when start new session.
     GetFocusedWebView(IpcSender<Option<WebViewId>>),
+    /// Get all webviews
+    GetAllWebViews(IpcSender<Result<Vec<WebViewId>, ErrorStatus>>),
     /// Check whether top-level browsing context is open.
     IsWebViewOpen(WebViewId, IpcSender<bool>),
     /// Check whether browsing context is open.
@@ -249,6 +251,7 @@ pub enum WebDriverScriptCommand {
     WillSendKeys(String, String, bool, IpcSender<Result<bool, ErrorStatus>>),
     AddLoadStatusSender(WebViewId, IpcSender<WebDriverLoadStatus>),
     RemoveLoadStatusSender(WebViewId),
+    GetWindowHandle(IpcSender<Result<String, ErrorStatus>>),
 }
 
 #[derive(Clone, Debug, Deserialize, Serialize)]