A2DP: Make sure CONNECT_TIMEOUT is scheduled in intermediate states

* Always schedule CONNECT_TIMEOUT message when entering Connecting and
  Disconnecting state
* Always remove CONNECT_TIMEOUT message when exting Connecting and
  Disconnecting state
* Add testIncomingTimeout in A2dpStateMachineTest to verify that an
  incoming connecting request could timeout as well

Bug: 73899051
Test: connect and disconnect to A2dp devices
      runtest -j32 bluetooth -c com.android.bluetooth.a2dp.A2dpStateMachineTest

Change-Id: I4412c77c8395a1ede12d7c1bd071822e55f5dd9c