Implement CallbackScope class

This is a wrapper class to support the following N-APIs.
  - napi_open_callback_scope()
  - napi_close_callback_scope()

Refs: https://nodejs.org/api/n-api.html#n_api_napi_open_callback_scope

napi-inl.h

@@ -3288,6 +3288,31 @@ inline Value EscapableHandleScope::Escape(napi_value escapee) {
   return Value(_env, result);
 }
 
+////////////////////////////////////////////////////////////////////////////////
+// CallbackScope class
+////////////////////////////////////////////////////////////////////////////////
+
+inline CallbackScope::CallbackScope(
+  napi_env env, napi_callback_scope scope) : _env(env), _scope(scope) {
+}
+
+inline CallbackScope::CallbackScope(napi_env env) : _env(env) {
+  napi_status status = napi_open_callback_scope(_env, nullptr, nullptr, &_scope);
+  NAPI_THROW_IF_FAILED_VOID(_env, status);
+}
+
+inline CallbackScope::~CallbackScope() {
+  napi_close_callback_scope(_env, _scope);
+}
+
+inline CallbackScope::operator napi_callback_scope() const {
+  return _scope;
+}
+
+inline Napi::Env CallbackScope::Env() const {
+  return Napi::Env(_env);
+}
+
 ////////////////////////////////////////////////////////////////////////////////
 // AsyncContext class
 ////////////////////////////////////////////////////////////////////////////////

napi.h

@@ -1597,6 +1597,21 @@ namespace Napi {
     napi_escapable_handle_scope _scope;
   };
 
+  class CallbackScope {
+  public:
+    CallbackScope(napi_env env, napi_callback_scope scope);
+    explicit CallbackScope(napi_env env);
+    virtual ~CallbackScope();
+
+    operator napi_callback_scope() const;
+
+    Napi::Env Env() const;
+
+  private:
+    napi_env _env;
+    napi_callback_scope _scope;
+  };
+
   class AsyncContext {
   public:
     explicit AsyncContext(napi_env env, const char* resource_name);