japanese/fcitx5-karukan: Add port: Japanese input method for fcitx5 powered by neural kana-kanji conversion

Karukan is a Japanese Input Method Engine for Linux that uses neural
kana-kanji conversion powered by llama.cpp. It provides a fcitx5 addon
for romaji-to-hiragana conversion and intelligent kana-kanji
conversion using small neural network models (auto-downloaded on first
use).

WWW: https://github.com/togatoga/karukan

Inspired by: openSUSE Tumbleweed (https://build.opensuse.org/package/show/openSUSE:Factory/karukan)