mecab: add support for the UTF-8 charset + refactor

[paveloom]

Description of changes

Make the output readable on most systems:

./result/bin/mecab
今日もしないとね。
今日    名詞,副詞可能,*,*,*,*,今日,キョウ,キョー
も      助詞,係助詞,*,*,*,*,も,モ,モ
し      動詞,自立,*,*,サ変・スル,未然形,する,シ,シ
ない    助動詞,*,*,*,特殊・ナイ,基本形,ない,ナイ,ナイ
と      助詞,接続助詞,*,*,*,*,と,ト,ト
ね      助詞,終助詞,*,*,*,*,ね,ネ,ネ
。      記号,句点,*,*,*,*,。,。,。

Things done

• Built on platform(s)
  • x86_64-linux
  • aarch64-linux
  • x86_64-darwin
  • aarch64-darwin
• For non-Linux: Is sandbox = true set in nix.conf? (See Nix manual)
• Tested, as applicable:
  • NixOS test(s) (look inside nixos/tests)
  • and/or package tests
  • or, for functions and "core" functionality, tests in lib/tests or pkgs/test
  • made sure NixOS tests are linked to the relevant packages
• Tested compilation of all packages that depend on this change using nix-shell -p nixpkgs-review --run "nixpkgs-review rev HEAD". Note: all changes have to be committed, also see nixpkgs-review usage
• Tested basic functionality of all binary files (usually in ./result/bin/)
• 23.11 Release Notes (or backporting 23.05 Release notes)
  • (Package updates) Added a release notes entry if the change is major or breaking
  • (Module updates) Added a release notes entry if the change is significant
  • (Module addition) Added a release notes entry if adding a new NixOS module
• Fits CONTRIBUTING.md.

[teto]

passed nixpkgs-review for me