Fix #4242.

Use --no-tty-default, if you want fzf to perform a TTY look-up instead of defaulting to /dev/tty.

Close #4148

  # This will no longer cause 'Vim: Warning: Output is not to a terminal'
  fzf --bind 'enter:execute:vim {}' > /tmp/foo

See https://github.com/junegunn/fzf/discussions/3792

This allows us to separately capture the standard error from fzf and its
child processes, and there's less chance of user errors of redirecting
the error stream and hiding fzf.

This commit enables cpu, mem, block, and mutex profling of the FZF
executable. To support flushing the profiles at program exit it adds
util.AtExit to register "at exit" functions and mandates that util.Exit
is used instead of os.Exit to stop the program.

Co-authored-by: Junegunn Choi <junegunn.c@gmail.com>