conf-files: rework conf_files_list_with_replacement()

conf-files: rework conf_files_list_with_replacement()

Previously, symlinks in the replacement was not chased, hence we may
inserted a path to outside of the root directory, or we may have wrong
judgement whether we should insert the replacement or not.

This makes the symlinks in the replacement also resolved.
Also, as the function is only used by tmpfiles and sysusers, this
enables CONF_FILES_REGULAR, CONF_FILES_CHASE_BASENAME, and
CONF_FILES_FILTER_MASKED_BY_SYMLINK flags.