move boost rng wrapper from sc to comphelper

so we can re-use it in other modules

Change-Id: I6057b1e955f745019fd48f91a754279df0f2b948
Reviewed-on: https://gerrit.libreoffice.org/9348
Reviewed-by: Thomas Arnhold <thomas@arnhold.org>
Tested-by: Thomas Arnhold <thomas@arnhold.org>