sort_natural does no natural sort

sort_natural is able to sort case-insensitively but does not sort numbers in the expected way.

The sort would e.g. return

• 10,11,2,3,4 instead of the expected 2,3,4,10,11
• z11,z2 instead of the expected z2,z11

The overall definition of "natural" sort seems to be "how a human would sort the list", so it is a little vague. But the consensus seems to be that natural sorting should sort by numbers, not by characters:

• https://en.wikipedia.org/wiki/Natural_sort_order
• https://www.php.net/manual/en/function.natsort.php
• https://blog.codinghorror.com/sorting-for-humans-natural-sort-order/
• https://www.tutorialspoint.com/natural-sort-in-javascript
• https://stackoverflow.com/q/4836710

The fallout is, e.g. that navigation lists sorted by liquid are in the wrong order. This is done in multiple Jekyll themes, for example

Start by locating the sort_natural implementation and any tests covering its ordering behavior. Verify the current results against the examples in the issue, then update the behavior so numeric portions sort by value, including values such as 10, 11, 2 and z11, z2; done means these cases produce the expected natural order.