webdriver: Implement send alert text (#38140)

Implement webdriver `SendAlertText` command

Tests:
https://github.com/longvatrong111/servo/actions/runs/16342669929
https://github.com/longvatrong111/servo/actions/runs/16342671477

cc: @xiaochengh

---------

Signed-off-by: batu_hoang <hoang.binh.trong@huawei.com>
Signed-off-by: batu_hoang <longvatrong111@gmail.com>

components/shared/embedder/webdriver.rs

@@ -166,6 +166,7 @@ pub enum WebDriverCommandMsg {
         IpcSender<Result<Option<String>, ()>>,
     ),
     GetAlertText(WebViewId, IpcSender<Result<String, ()>>),
+    SendAlertText(WebViewId, String),
     AddLoadStatusSender(WebViewId, IpcSender<WebDriverLoadStatus>),
     RemoveLoadStatusSender(WebViewId),
 }