Adapt new EthernetManager APIs in Settings.

EthernetManager is going to be moved to Connectivity mainline module and
new EthernetManager management APIs have been exposed. This CL adapts
new APIs in the settings in advance, the changes include:

1. use addInterfaceStateListener and removeInterfaceStateListener.
2. rely on the onInterfaceStateChanged callback to receive the Ethernet
   interface state update, to replace the getAvailableInterfaces and
   getConfiguration.
3. after the Ethernet mainline migration completes, Settings cannot
   access the platform resource such as config_ethernet_iface_regex,
   instead, check the availability of Ethernet interface by checking
   if either any of FEATURE_ETHERNET and FEATURE_USB_HOST is supported.

Bug: 210586283
Bug: 218798003
Test: m
Test: manually verify that device can access the Internet via Ethernet
Test: manually verify that device can share the Internet via Ethernet
      tethering
Test: make RunSettingsRoboTests ROBOTEST_FILTER=<modified test cases>
      EthernetTetherPreferenceControllerTest
      AllInOneTetherSettingsTest
Change-Id: I9e10481e1751975772a24db29568aa26bb85cd70