Add Euler-Mascheroni constant to the constants values

[Xyncgas]

There is currently E, Pi, Tau in System.Math.
However Euler-Mascheroni constant is no where to be found.

[Xyncgas]

https://ehfd.github.io/world-record/euler-mascheroni-constant/

[bernd5]

that should be reported in https://github.com/dotnet/runtime

[Xyncgas]

Thanks

[HaloFour]

That'd be a request for the runtime repo to add another constant member to the System.Math class.