Disallow modifying USB in Settings

Background
* The admin can disable signaling over USB
  on corporate owned device.

Changes
* If the admin has disabled signaling over
  USB, disable preferences in Settings to
  modify USB.
* Show policy transparency dialogs.

Manual Testing:
* Install TestDPC
* Set up as Device Owner
* Disable USB data signaling
* Verify Settings > Connected Devices
  > USB is disabled
* Verify Settings > Network & Internet
  > Hotspot & tethering > USB tethering
  is disabled
* Verify Developer options >
  USB debugging, default USB configurations
  and USB audio routing are disabled

Bug: 168301639
Test: Manual Testing
      make RunSettingsRoboTests -j ROBOTEST_FILTER=TetherSettingsTest
      make RunSettingsRoboTests -j
      ROBOTEST_FILTER=UsbAudioRoutingPreferenceControllerTest
      make RunSettingsRoboTests -j
      ROBOTEST_FILTER=UsbDefaultFragmentTest
      make RunSettingsRoboTests -j
      ROBOTEST_FILTER=DevelopmentSettingsDashboardFragmentTest
      make RunSettingsRoboTests -j
      ROBOTEST_FILTER=DefaultUsbConfigurationPreferenceControllerTest
      make RunSettingsLibRoboTests -j
      ROBOTEST_FILTER=EnableAdbPreferenceControllerTest

Change-Id: I3e8461ac37f406a407c874598335cde28fb89b2d
Merged-In: I3e8461ac37f406a407c874598335cde28fb89b2d