An earlier commit made this remove duplicates, which set the precedent
that this function is trying to canonically represent the _meaning_ of
the version constraints rather than exactly how they were expressed in
the configuration.
Continuing in that vein, now we'll also apply a consistent (though perhaps
often rather arbitrary) ordering to the terms, so that it doesn't change
due to irrelevant details like declarations being written in a different
order in the configuration.
The ordering here is intended to be reasonably intuitive for simple cases,
but constraint strings with many different constraints are hard to
interpret no matter how we order them so the main goal is consistency,
so those watching how the constraints change over time (e.g. in logs of
Terraform output, or in the dependency log file) will see fewer noisy
changes that don't actually mean anything.
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