WriteUtf8行为和v8保持一致

[chexiongsheng]

static void Print(const v8::FunctionCallbackInfo<v8::Value>& info) {
    //std::cout << "Print:" << info.Length() << std::endl;
    v8::Isolate* isolate = info.GetIsolate();
    v8::Local<v8::Context> context = isolate->GetCurrentContext();
    
    //std::cout << "len:" << info.Length() << std::endl;
    
    auto str = info[0]->ToString(context).ToLocalChecked();
    
    auto len = str->Utf8Length(isolate);
    //std::cout << "len:" << len << std::endl;
    UE_LOG(LogTemp, Warning, TEXT("len: %d"), len);
    char* data = new char[len + 1];
    data[len] = 111;
    str->WriteUtf8(isolate, data);
    //std::cout << "data[n]:" << (int)data[len] << std::endl;
    UE_LOG(LogTemp, Warning, TEXT("data[n]: %d"), (int)data[len]);
    
    std::string msg = *(v8::String::Utf8Value(isolate, str));
    //std::cout << msg << std::endl;
}

如上代码，用typescirpt调用

globalThis.Print('hello');

用v8时打印

LogTemp: Warning: len: 5
LogTemp: Warning: data[n]: 0

用backend-quickjs时打印

LogTemp: Warning: len: 5
LogTemp: Warning: data[n]: 111

简单来说v8会认为内存分配为Utf8Length + 1，并自动在str[Utf8Length] 添加0结尾。

[chexiongsheng]

这点差异导致某项目崩溃，该项目本来希望通过puerts那加修复：Tencent/puerts#1680
但这是应该属于backend-quickjs的bug

[chexiongsheng]

我看unity还是挺多地方用到WriteUtf8，比如这里：https://github.com/Tencent/puerts/blob/2881eace91871eb0ce6b164077ea344aa02ea8fa/unity/native_src/Src/PluginImpl.cpp#L433

不过这里带了长度了