In the `Visual Studio 15 2017` generator, if the `VS150COMNTOOLS`
environment variable points at a specific VS 2017 instance reported by
the Visual Studio Installer tool, use that as the preferred instance.
Inspired-by: Iyyappa Murugandi <iyyappam@microsoft.com>
Fixes: #16846
VS 2017 exports a COM component which can be queried to find if VS 2017
is installed and also other components such as VC toolset and Windows
SDKs. Add a helper class to interact with this interface.