Update to .NET 6?

Looks like TryFSharp uses some older version of F# (noticed by certain new .NET 6.0 methods not being available). Not sure what version, since the following snippet fails to run:

```f#
printfn "%A" System.Environment.Version // throws error: FABLE: Cannot resolve System.Environment.get_Version
```

It should be noted that the context-sensitive help just works, it recognizes `Environment.Version` just fine and shows its members.

PS, `System.Runtime.InteropServices.RuntimeInformation.FrameworkDescription` doesn't work either, since the Interop dll isn't available (afaict).

Start by locating TryFSharp's F# and .NET/Fable configuration, then reproduce the Environment.Version and RuntimeInformation.FrameworkDescription snippets from the issue. Done means the relevant .NET 6 APIs resolve and the existing build or test checks pass.

Written by the indexing model from the issue text.