Expose some APIs as test APIs to facilitate CTS

Test: added new cts tests
Bug: 123896388
Change-Id: I742f23be57e731307338591d816f7888e198b333
diff --git a/telecomm/java/android/telecom/Conference.java b/telecomm/java/android/telecom/Conference.java
index 7d1f8ce..6382acf 100644
--- a/telecomm/java/android/telecom/Conference.java
+++ b/telecomm/java/android/telecom/Conference.java
@@ -19,6 +19,7 @@
 import android.annotation.NonNull;
 import android.annotation.Nullable;
 import android.annotation.SystemApi;
+import android.annotation.TestApi;
 import android.net.Uri;
 import android.os.Bundle;
 import android.os.SystemClock;
@@ -571,6 +572,7 @@
      * @return The primary connection.
      * @hide
      */
+    @TestApi
     @SystemApi
     public Connection getPrimaryConnection() {
         if (mUnmodifiableChildConnections == null || mUnmodifiableChildConnections.isEmpty()) {