Update ImsPhoneCallTracker to detect situations where call will drop.

Add logic to set a property on incoming telephony connections if
answering the call will cause the active call to be disconnected.  This is
tied to carrier logic which requires that a wifi video call is dropped
when an incoming audio-only call is answered.  That same logic also
includes the provision that a call which has had video at some point in its
lifespan will be treated as a video call.

Bug: 29275420
Change-Id: Id9f58150a6bbd9894076913a880036a7e7fc6834