dircolors: add --print-ls-colors to display colored entries

dircolors: add --print-ls-colors to display colored entries

* NEWS: Mention the new feature.
* doc/coreutils.texi (dircolors invocation): Describe the new
--print-ls-colors option.
* src/dircolors.c (print_ls_colors): A new global to select
between shell or terminal output.
(append_entry): A new function refactored from dc_parse_stream()
to append the entry in the appropriate format.
(dc_parse_stream): Adjust to call append_entry().
* tests/misc/dircolors.pl: Add test cases.