[LyX/master] Japanese translations and docs from Koji

[Richard Kimberly Heck]

commit afcd501fe8f53202efe7c8d99dba86a38a081e70
Author: Richard Kimberly Heck <rikiheck at lyx.org>
Date:   Mon Dec 25 11:41:49 2023 -0500

    Japanese translations and docs from Koji

 lib/doc/ja/Additional.lyx    |   97 +++++--
 lib/doc/ja/Customization.lyx |  508 +++++++++++++++++++++++++++++--
 lib/doc/ja/Math.lyx          |  274 +++++++++++++++--
 lib/doc/ja/Tutorial.lyx      |   10 +-
 lib/doc/ja/UserGuide.lyx     |  324 +++++++++++++++-----
 po/ja.po                     |  681 +++++++++++++++++++++++-------------------
 6 files changed, 1423 insertions(+), 471 deletions(-)