Support disconnecting conference participants from conference.

- Added "onDisconnectConferenceParticipant" method used to inform a
connection acting as the conference host that one of the participants
should be disconnected.
- Added "VIRTUAL_CALL" PhoneCapability used to indicate that a call cannot
be the active or background call, but only be a child of another call.

Bug: 18228141
Bug: 18176606
Change-Id: I7aec631cc89c0f08e174b24ce3a9cb547b47e36b

telecomm/java/android/telecom/Connection.java

@@ -973,6 +973,15 @@ public abstract class Connection {
      */
     public void onDisconnect() {}
 
+    /**
+     * Notifies this Connection of a request to disconnect a participant of the conference managed
+     * by the connection.
+     *
+     * @param endpoint the {@link Uri} of the participant to disconnect.
+     * @hide
+     */
+    public void onDisconnectConferenceParticipant(Uri endpoint) {}
+
     /**
      * Notifies this Connection of a request to separate from its parent conference.
      */