Fix error header for bidirectional streaming models

Author: SergeyRyabinin

tools/code-generation/generator/src/main/resources/com/amazonaws/util/awsclientgenerator/velocity/cpp/ErrorsHeader.vm

@@ -79,5 +79,19 @@ namespace ${metadata.classNamePrefix}ErrorMapper
   ${CppViewHelper.computeExportValue($metadata.classNamePrefix)} Aws::Client::AWSError<Aws::Client::CoreErrors> GetErrorForName(const char* errorName);
 }
 
+#set($modeledCommonErrors = [])
+#foreach($shapeEntry in $serviceModel.shapes.entrySet())
+#if($shapeEntry.value.isException() && !$shapeEntry.value.isModeledException())
+#set($addArgDummy = $modeledCommonErrors.add($shapeEntry.key))
+#end
+#end
+#if(!$modeledCommonErrors.isEmpty())
+namespace Model {
+#foreach($errorName in $modeledCommonErrors)
+using $errorName = Aws::Client::AWSError<TranscribeStreamingServiceErrors>;
+#end
+}  // namespace Model
+
+#end
 } // namespace ${serviceNamespace}
 } // namespace ${rootNamespace}