Add FlatbufferToJson overload for aos::fbs::Builder<T>

Change-Id: If56247f8b86213d813345ade82bf1bcdf9976e97
Signed-off-by: James Kuszmaul <james.kuszmaul@bluerivertech.com>
diff --git a/aos/json_to_flatbuffer.h b/aos/json_to_flatbuffer.h
index 6ef3544..deafaa7 100644
--- a/aos/json_to_flatbuffer.h
+++ b/aos/json_to_flatbuffer.h
@@ -75,6 +75,12 @@
       Flatbuffer<T>::MiniReflectTypeTable(), json_options);
 }
 
+template <typename T, typename Enable = T::Flatbuffer>
+inline ::std::string FlatbufferToJson(const fbs::Builder<T> &flatbuffer,
+                                      JsonOptions json_options = {}) {
+  return FlatbufferToJson(flatbuffer.AsFlatbufferSpan(), json_options);
+}
+
 // Converts a flatbuffer::Table to JSON.
 template <typename T>
 typename std::enable_if<