More telephony updates for mainline.

Add new TelecomManager#getDefaultDialerPackage which is multiuse aware;
this is used when showing the voicemail notification.
Remove some @hide methods from Conference; push these inline.
Move ConferenceParticipantConnection into frameworks/opt/net/ims since
it is just an IMS implementation detail.

Bug: 141576016
Test: Manual smoke test.
Test: Run unit tests.
Test: Run CTS tests.
Change-Id: I39b6955cb14cc1ca68b05c620c3d09a2cdfe30c9

core/java/android/provider/CallLog.java

@@ -227,7 +227,7 @@ public class CallLog {
 
         /**
          * Indicates the call underwent Assisted Dialing.
-         * @hide
+         * @see TelecomManager#EXTRA_USE_ASSISTED_DIALING
          */
         public static final int FEATURES_ASSISTED_DIALING_USED = 1 << 4;