Use isConnected in CachedBluetoothDevice

This method check whether it has connected profile, not physical
connection between devices.

It make more sense to use it in settings:
1. We only care about whether it has active profile(i.e. A2dp, hfp..)
2. Sometime when profile is disconnected, BluetoothDevice.isConnected()
still return true. This may make UI flaky.

Bug: 79947085
Test: RunSettingsRoboTests
Change-Id: I44039704508a742c7a8aef0a035afcf169b08939