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_instance_data/binding.gyp

@@ -3,7 +3,6 @@
     {
       "target_name": "test_instance_data",
       "sources": [
-        "../entry_point.c",
         "test_instance_data.c"
       ]
     }

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

@@ -1,7 +1,8 @@
+#include <js_native_api.h>
 #include <stdio.h>
 #include <stdlib.h>
-#include <js_native_api.h>
 #include "../common.h"
+#include "../entry_point.h"
 
 typedef struct {
   size_t value;