`dnup` should use an atomic move operation if the dotnet_root folder is empty

We want to avoid possible installation issues if the dnup process is killed/closed/system shuts down in the middle of install. This is protected by a mutex / the manifest but for the install library which simplifies installation and avoids using the mutex and dnup manifest, we could be vulnerable to these issues. What we should do for the standalone installs to a private folder to reduce these issues is make the extraction logic separate in a temp folder, and then use a move operation to make it as atomic as possible.

Separately, we should try to minimize the operations to as many atomic folder moves as possible. It cant all be an atomic move because of the fact that the dotnet.exe (host) shouldn't be replaced, (nor the other older install version folders) that exist in dotnet_root if it's not empty.