Rework the VS version evaluation

Rework the VS version evaluation

For the latest versions, refer also to the Visual Studio version, not to
the exact toolset version. The latest Visual Studio versions are moving
fast and the method existed previously is not sutable to keep up
anymore. Instead of refering to the exact toolset, it refers to the
Visual Studio version and implies the latest toolset available there.
That is still not ideal, another situation can arise where VS version is
not changed, but the toolset version is. It might be better to refer to
it a generic way in the future or even omit at all, and improve the
internal compatibility checks instead.