This is just a set of C functions accessing public libxmlsec API, it's
perfectly OK to have this in xmlsecurity/ instead of patching the
bundled libxmlsec for this.

Change-Id: Ib3e746883a47b80626fdcd64149ce50aa0588395
Reviewed-on: https://gerrit.libreoffice.org/40209Reviewed-by: Miklos Vajna <vmiklos@collabora.co.uk>
Tested-by: Jenkins <ci@libreoffice.org>