interface class provides TRANSACTION_<methodname> consts

Like the Java and the rust backends, cpp and cpp_ndk backends now also
provide transaction codes as TRANSACTION_<method> consts in the
interface class.

Bug: 174187767
Test: aidl_unittests
Change-Id: Ic6f15db21e1af0e03cb690b0e6488d6f697dc080
diff --git a/aidl_to_cpp.h b/aidl_to_cpp.h
index a6597f9..f6974f5 100644
--- a/aidl_to_cpp.h
+++ b/aidl_to_cpp.h
@@ -34,7 +34,7 @@
   const bool isPointer;           // whether the variable 'name' is a pointer or not
 };
 
-std::string GetTransactionIdFor(const AidlMethod& method);
+std::string GetTransactionIdFor(const AidlInterface& iface, const AidlMethod& method);
 
 std::string CppNameOf(const AidlTypeSpecifier& type, const AidlTypenames& typenames);