bug#64941: ModuleNotFoundError in ibus-anthy

[elaexuotee]

Some headway: It looks like anthyprefs sits under a different directory than
the engine script:

    $ guix shell --pure ibus ibus-anthy

    $ ls $GUIX_ENVIRONMENT/share/ibus-anthy/setup/
    __pycache__/  _config.py  anthyprefs.py  main.py  prefs.py  setup.ui

    $ ls $GUIX_ENVIRONMENT/share/ibus-anthy/engine/
    __pycache__/  _config.py  default.xml  engine.py  factory.py  jastring.py
    kana.py  main.py  romaji.py  segment.py  tables.py  thumb.py

Manually running the engine with a PYTHONPATH fixes the error:

    $ PYTHONPATH=$GUIX_ENVIRONMENT/share/ibus-anthy/setup 
$GUIX_ENVIRONMENT/libexec/ibus-engine-anthy

However, starting ibus-daemon with PYTHONPATH doesn't do anything. I'm guessing
that the environment variable doesn't propagate to engine exec commands. Maybe
a problem in the ibus-engine-anthy wrapper script?