Apply @hide / @SystemApi to android.telecom.*

Move the android.telecom.* namespace back to @hide, and also mark it
with @SystemApi so that system-privileged apps can use them.

Bug: 18302450
Change-Id: I33ae1b9b0dfdb1c5eff51ca3c829196bcfc9411c

telecomm/java/android/telecom/Connection.java

@@ -19,6 +19,7 @@ package android.telecom;
 import com.android.internal.telecom.IVideoCallback;
 import com.android.internal.telecom.IVideoProvider;
 
+import android.annotation.SystemApi;
 import android.net.Uri;
 import android.os.Handler;
 import android.os.IBinder;
@@ -43,7 +44,9 @@ import java.util.concurrent.ConcurrentHashMap;
  * Implementations are then responsible for updating the state of the {@code Connection}, and
  * must call {@link #destroy()} to signal to the framework that the {@code Connection} is no
  * longer used and associated resources may be recovered.
+ * @hide
  */
+@SystemApi
 public abstract class Connection {
 
     public static final int STATE_INITIALIZING = 0;