Introduce APIs for RTT calls (part 1)

Add signaling methods and data pipes for handling real-time text during
a call.

Change-Id: I876827c448252c5f786d7a4919c47891acb03877
Test: manual, through telecom testapps

telecomm/java/android/telecom/Phone.java

@@ -201,6 +201,13 @@ public final class Phone {
         }
     }
 
+    final void internalOnRttUpgradeRequest(String callId, int requestId) {
+        Call call = mCallByTelecomCallId.get(callId);
+        if (call != null) {
+            call.internalOnRttUpgradeRequest(requestId);
+        }
+    }
+
     /**
      * Called to destroy the phone and cleanup any lingering calls.
      */