Replace the hidden API to public API or other alternatives

Some of connectivity related files are going to be a part of
mainline module, so the external callers cannot call its hidden
API.
Replace the hidden API to public API or other alternatives from
the callers side.

Bug: 182859030
Test: 1. Remove "framework-connectivity.impl"
      2. atest SettingsUnitTests:InternetUpdaterTest
      3. atest SettingsUnitTests:ProviderModelSliceHelperTest
      4. atest SettingsUnitTests:MobileNetworkUtilsTest
      5. make RunSettingsRoboTests \
         ROBOTEST_FILTER=AppDataUsagePreferenceControllerTest
      6. make RunSettingsRoboTests \
         ROBOTEST_FILTER=TetherPreferenceControllerTest
      7. make RunSettingsRoboTests \
         ROBOTEST_FILTER=WifiDetailPreferenceController2Test
      8. make RunSettingsRoboTests \
         ROBOTEST_FILTER=ContextualWifiSliceTest
Change-Id: Idd1ca57d8f2790070e9c401936c5af2a05bcfe9d