Motivation for this change

The goal is helping to package dotnet projects similar to node2nix or pypi2nix

After dotnet restore, produces the file project.assets.json listing each nuget package with sha512. fetchurl supports sha512, so it is just forwarded.
Using this, an expression can be created containing all nuget dependencies.

Things done

There are no packages yet which would use sha512 in fetchNuGet, so I have tested this way:

nix repl .
Added 9404 variables.

nix-repl> :b dotnetPackages.Fake 

Which still builds and uses the cache.

I have tested with the same version and sha512 here

• Tested using sandboxing (nix.useSandbox on NixOS, or option sandbox in nix.conf on non-NixOS)
• Built on platform(s)
  • NixOS
  • macOS
  • other Linux distributions
• Tested via one or more NixOS test(s) if existing and applicable for the change (look inside nixos/tests)
• Tested compilation of all pkgs that depend on this change using nix-shell -p nox --run "nox-review wip"
• Tested execution of all binary files (usually in ./result/bin/)
• Determined the impact on package closure size (by running nix path-info -S before and after)
• Fits CONTRIBUTING.md.