uv-resolver: sort in `format_terms`
This makes use of the newly added `Ord` impl on `PubGrubPackage` to make
the output of `format_terms` independent of hashmap iteration order.
This was already collecting the terms into an intermediate `Vec`, so
sorting probably isn't going to add any significant overhead here.
(Plus, this is only running when formatting an error message after a
solution could not be found, so an extra sort doesn't seem like a big
deal here.)
Note that some tests are updated in this commit as a result of this
change. As far as I can tell, the semantic meaning of the output remains
the same. But the order of the listed packages does not.
Specific thing motivating this change is, in a subsequent, I added
`Option<MarkerTree>` to `PubGrubPackage::Package`, and this caused
similar changes in test output. So I backtracked and isolated this
change from the addition of `Option<MarkerTree>`.
