Prevent leaking Wi-Fi dialog on lock screen

- The Wi-Fi dialog is designed to be displayed on the system UI

- Dismiss Wi-Fi dialog to prevent leaking user data on lock screen

Bug: 231583603
Test: manual test
make RunSettingsRoboTests ROBOTEST_FILTER=WifiDialogActivityTest

Change-Id: Ie67ff1138ffeddd3e358331d8cef61e0629173e2