[gdb/cli] Add a progress meter

Add a progress meter.  It's not used anywhere yet.

gdb/ChangeLog:

2020-12-16  Tom Tromey  <tom@tromey.com>
	    Tom Tromey  <tromey@redhat.com>
	    Tom de Vries  <tdevries@suse.de>

	* utils.h (get_chars_per_line): Declare.
	* utils.c (get_chars_per_line): New function.
	(fputs_maybe_filtered): Handle '\r'.
	* ui-out.h (ui_out::progress_meter): New class.
	(ui_out::progress, ui_out::do_progress_start)
	(ui_out::do_progress_notify, ui_out::do_progress_end): New
	methods.
	* ui-out.c (do_progress_end)
	(make_cleanup_ui_out_progress_begin_end, ui_out_progress): New
	functions.
	* mi/mi-out.h (mi_ui_out::do_progress_start)
	(mi_ui_out::do_progress_notify, mi_ui_out::do_progress_end): New
	methods.
	* cli-out.h (struct cli_ui_out) <do_progress_start,
	do_progress_notify, do_progress_end>: New methods.
	<enum meter_stat, struct cli_progress_info>: New.
	<m_meters>: New member.
	* cli-out.c (cli_ui_out::do_progress_start)
	(cli_ui_out::do_progress_notify, cli_ui_out::do_progress_end): New
	methods.