Connectivity: Update Settings Wifi subpage interactive test

This change enhances the existing
WifiInteractiveUiTest.EnableDisableFromOsSettings test to fully replace
the wifi.StatusUI OS Settings wifi page tast test.
These updates include:

- Checking that the WIFI scanning spinner is shown/hidden.
- Checking that the list of networks is shown/hidden.
- Checking "Searching for networks..." message is shown/hidden.
  - Use its parent to check when hidden since display none is set there.

Bug: 370817960
Test: interactive_ui_tests --gtest_filter=WifiInteractiveUiTest.ToggleAndCheckOsSettingsWiFiPageElements
Change-Id: Id8eab2fc32f0f2f04a895322e6c9611570bdb6ab
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5954177
Commit-Queue: Xiangdong Kong <xiangdongkong@google.com>
Reviewed-by: Chad Duffin <chadduffin@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1378017}