SYSDB: Internally expose sysdb_search_ts_matches()
    
    This function will be used in the follow-up patches. As it's going to be
    "exposed", let's also rename it from search_ts_matches() to
    sysdb_search_ts_matches().
    
    Related:
    https://pagure.io/SSSD/sssd/issue/3369
    
    Signed-off-by: Fabiano Fidêncio <fidencio@redhat.com>
    
    Reviewed-by: Jakub Hrozek <jhrozek@redhat.com>
    (cherry picked from commit 347be58e1769ba90b49a7e5ec1678ef66987f6cd)