Add a general command to scan user computer

In the current situation,  the Qt library in `vcpkg` is checked on startup and added as an `additionalQtPath` if the user sets it via the message box. But after the startup, there is no way to scan or add it. 

A general scan command in `qt-core` would be useful so that users can scan their computer when needed. That command can also include the `Qt: Scan For Qt kits`  command.