tex-texdoc{,-doc}: update to 4.0.1

This is a Texdoc update aiming to be contained in TeX Live 2023.

Major changes
- Online search feature is added:
  users using TL without documentation will be sent to texdoc.org
- Add new action --print-completion:
  for the moment, only zsh is supported. Contributions welcome.

Minor fixes and tweaks
- Reflect environment variables (e.g., LANGUAGE, LC_ALL, and LANG)
  before checking system locale
- Line continuation with tailing backslashes in config files
- Scoring adjustments
- Documentation tweaks

(markd)