Add Call answered key in TelecomManager.java

The key is used for dialer apps to know when call is answered by user.

Test: N/A
Change-Id: Idfef41b88df21a9a39032fdbb4090a181b164f73
Skip-CP-To-Master: pending on telecom review
Bug: 242074284

telecomm/java/android/telecom/TelecomManager.java

@@ -411,6 +411,15 @@ public class TelecomManager {
     public static final String EXTRA_CALL_CREATED_TIME_MILLIS =
             "android.telecom.extra.CALL_CREATED_TIME_MILLIS";
 
+    /**
+     * Optional extra for incoming containing a long which specifies the time the
+     * call was answered by user. This value is in milliseconds.
+     * @hide
+     */
+    public static final String EXTRA_CALL_ANSWERED_TIME_MILLIS =
+            "android.telecom.extra.CALL_ANSWERED_TIME_MILLIS";
+
+
     /**
      * Optional extra for incoming and outgoing calls containing a long which specifies the Epoch
      * time the call was created.