Update git submodules

* Update helpcontent2 from branch 'master'
  - Database files should appear with app:"BASE" in instdir/help/*/bookmarks.js
    
    ...instead of with app:"SHARED", according to a request by buovjaga.
    
    That means that helpcontent2/source/text/shared/explorer/database/*.xhp files
    (and their per-locale counterparts) should be processed into workdir/
    CustomTarget/helpcontent2/help3xsl/shared/explorer/database/*/bookmarks.part
    (which were empty until now) instead of
    workdir/CustomTarget/helpcontent2/help3xsl/shared/*/bookmarks.part.
    
    This change requres gb_AllLangHelp_*_BOOKMARK_HELPFILES introduced into the core
    repo with <https://gerrit.libreoffice.org/#/c/63364/> "Prepare
    gb_AllLangHelp_add_helpfiles for special bookmark needs".
    
    Change-Id: I8f37fcec67a37aee4260042e550214a34495254a
    Reviewed-on: https://gerrit.libreoffice.org/63365
    Tested-by: Jenkins
Reviewed-by: Stephan Bergmann <sbergman@redhat.com>
    

helpcontent2 @ 6a39aed4

-Subproject commit 3984e2baefed611f79a36b85f3884a8cc2779653
+Subproject commit 6a39aed4a3bec2ef053371eff3199f6de1f46874