MSBuild SDK format

[scottdorman]

Investigate moving this to be an MSBuild SDK that can be included in each project through a NuGet reference, which will automatically include the relevant files. I think this should be possible to do, at least for the pieces of generating the ThisAssembly file and updating all of the build properties for the version numbers. The logic for generating the version number information into the output file may need to become a dotnet CLI tool though, which it probably should anyway.