Motivation for this change

This adds the "Kreative Square" font, which is one of a handful of fonts in existence that have a perfect square appearance (width == height). There are actually 2 fonts. Below are their upstream descriptions:

• Kreative Square is the main variant. Use this one if possible.
• Kreative Square SM removes all characters not the same width as basic ASCII (combining characters, double-width characters, fixed-width spaces, etc.) for braindead programs that determine if a font is monospaced from its advance widths and not its PANOSE values (GNOME Terminal does this)."

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.

I've built and installed this package and tested it by actually trying to use it in my Alacritty terminal, which worked.