fdo#68849: Add header guards to all include files

Added header guards to files in directory svx/

Change-Id: I1c2006bccf03c3057daf6ea2711c52a8c1f455f3
Reviewed-on: https://gerrit.libreoffice.org/9586
Reviewed-by: Thomas Arnhold <thomas@arnhold.org>
Tested-by: Thomas Arnhold <thomas@arnhold.org>