add net48 without system.reflection.metadata

[bruno-garcia]

We had a few customers sharing challenges when building for net48 because of dependencies.

This is an attempt to reduce dependencies when building specifically for newer .NET Framework.

I also believe we should bump the min version to 6.0.0 (as opposed to 5.0.0 which we have now and is deprecated):

https://www.nuget.org/packages/System.Reflection.Metadata/6.0.0#dependencies-body-tab