A number of client programs have a "--progress" option that when printing
to a TTY, updates the current line by printing a '\r' and overwriting it.
After the last line, '\n' needs to be printed to move the cursor to the
next line. pg_basebackup and pgbench got this right, but pg_rewind and
pg_checksums were slightly wrong. pg_rewind printed the newline to stdout
instead of stderr, and pg_checksums printed the newline even when not
printing to a TTY. Fix them, and also add a 'finished' argument to
pg_basebackup's progress_report() function, to keep it consistent with
the other programs.

Backpatch to v12. pg_rewind's newline was broken with the logging changes
in commit cc8d4151 in v12, and pg_checksums was introduced in v12.

Discussion: https://www.postgresql.org/message-id/82b539e5-ae33-34b0-1aee-22b3379fd3eb@iki.fi