Floss: handle unbonding device doesn't report disconnection to CRAS

In aosp/2685489 we tried to be aggressive to disconnect audio profile
connection attempt from an unbonded device. However, the function
confuses this state with user forgetting the device via BT menu, since
both involves unbonded device and empty task queue. In case of the
latter, we would still try to invoke DisconnectDevice, but at the risk
of not informing CRAS, depending on the order of profile disconnection.

This CL also checks for the media state when determining the two cases
above. To be precise, when the state is FullyConnected, it could only
mean the latter case. On the other hand, if the state is Disconnecting,
it could mean both cases, but when it's the latter case, we can be sure
that CRAS has been informed of the disconnection.

Bug: 358525472
Test: m -j
Test: Using the latest pixel buds, do this multiple times.
      (1) Pair using fast pair
      (2) Verify the device doesn't immediately disconnect
      (3) Forget the device (skipping decive disconnection)
      (4) Sign out and sign in again
Flag: EXEMPT, floss only changes

Change-Id: I80ebb475743e9f902b5a8ecd2bd8021d7793584d