For adding tag, allow filtering on buildrequires to find out koji_tags from tag inheritance
    
    The original AddTagHandler.get_match_tags_in_inheritance finding out module's
    koji_tags added to tag inheritance should also allow filtering modules on
    buildrequires.
    
    On the other hand, this method is duplicated with existing method
    find_module_tags_from_koji_inheritance. So the solution is to promote
    find_module_tags_from_koji_inheritance to BaseHandler and be reusable for both
    of the handlers.
    
    Signed-off-by: Chenxiong Qi <cqi@redhat.com>