Agda: 2.4 -> 2.5.1 (new)

[laMudri]

Motivation for this change

#15696 was messy and acquired a merge commit. This should be ready to merge as-is.

Things done

• Tested using sandboxing
  (nix.useSandbox on NixOS,
  or option build-use-sandbox in nix.conf
  on non-NixOS)
• Built on platform(s)
  • NixOS
  • OS X
  • Linux
• 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/)
• Fits CONTRIBUTING.md.

@peti

[mention-bot]

By analyzing the blame information on this pull request, we identified @joachifm, @dezgeg and @Fuuzetsu to be potential reviewers

[copumpkin]

Thanks!