Motivation for this change

Shortly after v2.16 was released, a single commit was added to master
that adds support for mounting LUKS2 volumes which is now the default
for cryptsetup. This adds that.

As there is no easy way to fetch that commit as a patch, I have added it
to nixpkgs.

Tested on both LUKS1 and LUKS2 volumes.

Also some build cleanups.

Things done

• Tested using sandboxing (nix.useSandbox on NixOS, or option sandbox in nix.conf on non-NixOS linux)
• 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 nixpkgs-review --run "nixpkgs-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)
• Ensured that relevant documentation is up to date
• Fits CONTRIBUTING.md.