For refs and reflogs, we need to scan its corresponding directories to check every regular file or symbolic link which shares the same pattern. Introduce a unified interface for scanning directories for files-backend. Mentored-by: Patrick Steinhardt <ps@pks.im> Mentored-by: Karthik Nayak <karthik.188@gmail.com> Signed-off-by: shejialuo <shejialuo@gmail.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>