XML Handler

A number of issues with the XML functions in the state environment.

- Successive "RemoveAttribute" calls result in:
"
Exception thrown: read access violation.
**this** was 0x68.
"
- SaveToString calls once an attribute has been removed and then added throws the same error
- SaveToString calls can duplicate "xmlns=..."

This error can be repeated by including an XML file in the resource folder and using this code:

auto xml_string = pStateEnvironment->LoadResourceString("test");
auto xml_object = pStateEnvironment->ParseXMLString(xml_string);
auto xml_string_back = xml_object->SaveToString(false);

首先，使用 issue 中所示的 XML 資源以及對 LoadResourceString、ParseXMLString、RemoveAttribute 和 SaveToString 的呼叫來重現報告。追蹤連續移除屬性以及移除後再新增的序列化過程，然後驗證 SaveToString 不再當機，也不會重複產生 xmlns 項目。

由索引模型根據 Issue 內容生成。