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>

ports/servoshell/desktop/app.rs

@@ -620,6 +620,9 @@ impl App {
                         warn!("Failed to send response of GetAlertText: {error}");
                     };
                 },
+                WebDriverCommandMsg::SendAlertText(webview_id, text) => {
+                    running_state.set_alert_text_of_newest_dialog(webview_id, text);
+                },
                 WebDriverCommandMsg::TakeScreenshot(..) => {
                     warn!(
                         "WebDriverCommand {:?} is still not moved from constellation to embedder",