Add support for Linux ARM and Alpine

[NTaylorMullen]

Much like dotnet/vscode-csharp#2771 we will need to do work to properly acquire the "right" bits for ARM scenarios.

We need to adjust the dynamic acquisition logic to get a compatible version of the runtime for either ARM or Alpine. (On first check, Alpine appeared to work when using the .NET Core image – I have not checked ARM, however.) We briefly describe the issue and how this can be detected here.