support custom code style preference in project settings

we can import codestyle into qtcreator, and then select it as project settings.
but the qt2.xml is imported as qtcreator's config, but not porject's.

If we can import or set code style as native project settings, but not reference qtcreator's global codestyle, it would be great!

If so, we can assign code style as project settings in the code repo, which can be loaded as project settings by qtcreator automatically.

```
<valuemap type="QVariantMap" key="EditorConfiguration.CodeStyle.0">
<value type="QString" key="language">Cpp</value>
<valuemap type="QVariantMap" key="value">
<value type="QByteArray" key="CurrentPreferences">CppGlobal</value>
</valuemap>
</valuemap>
```