This is a not-particularly-important "cleanliness" PR. It removes the
last remnants of the `x/exp` package, where we used the `maps.Keys`
function.
The original returned the keys in a slice, but when it became 'native'
the signature changed to return an iterator, so the new idiom is
`slices.Collect(maps.Keys(theMap))`, unless of course the raw iterator
can be used instead.
In some cases, where we previously collect into slice and then sort, we
can now instead do `slices.SortXX` on the iterator instead, making the
code a bit more concise.
This PR might be _slighly_ less optimal, because the original `x/exp`
implementation allocated the slice at the correct size off the bat,
which I suppose the new code won't.
Putting it up for discussion.
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Co-authored-by: Felix Lange <fjl@twurst.com>
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