CoreLib doesn't implement Environment.GetEnvironmentVariable and friends

[MichalStrehovsky]

GetEnvironmentVariable and ExpandEnvironment are implemented like this:

public static String GetEnvironmentVariable(String variable)
{
    if (variable == null)
        throw new ArgumentNullException("variable");

    // Environment variable accessors are not approved modern API.
    // Behave as if the variable was not found in this case.
    return null;
}

We need real implementations.

[weshaggard]

Yes that was their implementation for UWP. I agree we need this supported for this scenario. @AlexGhiondea should be able to handle it.

[MichalStrehovsky]

We might need to at least look at this in terms of the demo.

System.Console uses this for various things. I didn't investigate it now fully, but this did show up at some point when I did the original Hello World ILToCpp bringup. It's possible it was only needed for colors, but I don't remember anymore.

[AlexGhiondea]

I have a hacked version of this working on windows already. I will finalize it tomorrow and then I'll get the PAL implemented on Linux (we already have a cross plat implementation in CoreCLR for this).