doc: update attributes used by n-api samples (nodejs#35220)

Update n-api samples to create object properties matching to the JS defaults.

Using non configurable, non writable properties has its usecases but
the JS default for class methods is `configurable` and `writable`.
Js properties set by JS code `obj.prop = val` are `configurable`, `writable`
and `enumerable`.

doc/api/n-api.md

@@ -1777,8 +1777,16 @@ provided by the addon:
 ```c
 napi_value Init(napi_env env, napi_value exports) {
   napi_status status;
-  napi_property_descriptor desc =
-    {"hello", NULL, Method, NULL, NULL, NULL, napi_default, NULL};
+  napi_property_descriptor desc = {
+    "hello",
+    NULL,
+    Method,
+    NULL,
+    NULL,
+    NULL,
+    napi_writable | napi_enumerable | napi_configurable,
+    NULL
+  };
   status = napi_define_properties(env, exports, 1, &desc);
   if (status != napi_ok) return NULL;
   return exports;
@@ -1805,7 +1813,7 @@ To define a class so that new instances can be created (often used with
 napi_value Init(napi_env env, napi_value exports) {
   napi_status status;
   napi_property_descriptor properties[] = {
-    { "value", NULL, NULL, GetValue, SetValue, NULL, napi_default, NULL },
+    { "value", NULL, NULL, GetValue, SetValue, NULL, napi_writable | napi_configurable, NULL },
     DECLARE_NAPI_METHOD("plusOne", PlusOne),
     DECLARE_NAPI_METHOD("multiply", Multiply),
   };
@@ -3719,8 +3727,8 @@ if (status != napi_ok) return status;
 
 // Set the properties
 napi_property_descriptor descriptors[] = {
-  { "foo", NULL, NULL, NULL, NULL, fooValue, napi_default, NULL },
-  { "bar", NULL, NULL, NULL, NULL, barValue, napi_default, NULL }
+  { "foo", NULL, NULL, NULL, NULL, fooValue, napi_writable | napi_configurable, NULL },
+  { "bar", NULL, NULL, NULL, NULL, barValue, napi_writable | napi_configurable, NULL }
 }
 status = napi_define_properties(env,
                                 obj,