Create BluetoothSwitchPreference

In the new design, bluetooth preference is not MasterSwitchPreference
any more. This cl creates BluetoothSwitchPreference while reuse the
BluetoothEnabler.

Future cl will remove the BluetoothMasterSwitchPreference when P
feature is finalized.

Bug: 69333961
Test: RunSettingsRoboTests
Change-Id: Ie1f934b4e93a6758a1b0cf83bb5098585a635c2a