[LyX/master] Adapt French docs to new index features

[Juergen Spitzmueller]

commit 4299d842e871a8d3b93a10efbc1f18e7cc17ccdb
Author: Juergen Spitzmueller <spitz at lyx.org>
Date:   Fri Nov 4 09:03:55 2022 +0100

    Adapt French docs to new index features

 lib/doc/fr/EmbeddedObjects.lyx | 2609 ++++++++++++++++++---
 lib/doc/fr/Math.lyx            | 5049 ++++++++++++++++++++++++++++++++++++----
 lib/doc/fr/UserGuide.lyx       | 4153 +++++++++++++++++++++++++++++----
 3 files changed, 10565 insertions(+), 1246 deletions(-)