ref-filter.h: add functions for filter/format & format-only
Add two new public methods to 'ref-filter.h':
* 'print_formatted_ref_array()' which, given a format specification & array
of ref items, formats and prints the items to stdout.
* 'filter_and_format_refs()' which combines 'filter_refs()',
'ref_array_sort()', and 'print_formatted_ref_array()' into a single
function.
This consolidates much of the code used to filter and format refs in
'builtin/for-each-ref.c', 'builtin/tag.c', and 'builtin/branch.c', reducing
duplication and simplifying the future changes needed to optimize the filter
& format process.
Signed-off-by: Victoria Dye <vdye@github.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>