ls: improve alignment of quoted names

ls: improve alignment of quoted names

This provides better alignment when some names are quoted,
which also provides better indication that quotes are not
part of the name.

* src/ls.c (align_variable_outer_quotes): A new variable
set when ls is aligning columns (not using -m, non-zero -w),
and has a variable quoting style (shell, shell-escape, c-maybe).
(quote_name_buf): Writes to buffer rather than FILE,
taking care to avoid data copying if possible.  Refactored from...
(quote_name): ...here.  This now manages the buffer passed
to quote_name_buf() and outputs the padding, colors and name
in the appropriate order, while managing the --dired offsets.
(get_color_indicator): A new function to return the color sequence,
refactored from...
(print_color_indicator): ...here.  This now simply outputs.
(print_dir): Refactor common parts to quote_name().
(clear_files): Reset the flag indicating at least one
file is quoted in the current directory.
(needs_quoting): A new function to indicate at the scan stage
whether a name needs quoting.  Called from...
(gobble_file): ...here, until we find the first quoted file.
(print_name_with_quoting): Mostly refactored to quote_name().
* tests/ls/quote-align.sh: A new test for various output formats.
* tests/local.mk: Reference the new test.
* NEWS: Mention the improvement.