move "generate union code" to aidl_to_cpp_common
This is a preparation to add NDK backend for union.
Bug: 170784707
Bug: 150948558
Test: aidl_unittests / aidl_integration_test
Change-Id: I347fc7e114b84eb03baf826c86388176d90bc81e
diff --git a/aidl_unittest.cpp b/aidl_unittest.cpp
index ddfa0a5..3dd4e62 100644
--- a/aidl_unittest.cpp
+++ b/aidl_unittest.cpp
@@ -2701,6 +2701,7 @@
#include <binder/Parcel.h>
#include <binder/Status.h>
#include <cstdint>
+#include <type_traits>
#include <utility>
#include <variant>
#include <vector>