test: avoid copying test source files

Converting the helper functions to be inlined and making the helper file
header only.

PR-URL: https://github.com/nodejs/node/pull/49515
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Gabriel Schulhof <gabrielschulhof@gmail.com>

test/js-native-api/test_dataview/test_dataview.c

@@ -1,6 +1,7 @@
 #include <js_native_api.h>
 #include <string.h>
 #include "../common.h"
+#include "../entry_point.h"
 
 static napi_value CreateDataView(napi_env env, napi_callback_info info) {
   size_t argc = 3;