[Wi-Fi] Add STA+AP information in Hotspot & tethering footer

Use WifiManager#isStaApConcurrencySupported() to check if a
device supports STA+AP and shows the footer information.

Bug: 121328949
Test: make RunSettingsRoboTests ROBOTEST_FILTER=TetherSettingsTest
      make RunSettingsRoboTests ROBOTEST_FILTER=WifiTetherFooterPreferenceControllerTest
Change-Id: I3446abb5cc9cdf76da8d17f5de31bd65715c165c