I was reminded of this yesterday with unprintable characters as I
debugged some things on Windows. Inspired by Yarn, this change adds
a new flag --emoji (-e for short) that can be used to control whether
we show ASCII-only characters or not in the console. On Mac, it
defaults to true, and on Windows and Linux, it defaults to false.
This also brings back the retro ASCII-friendly progress spinner
when --emoji is disabled.
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