Add a recursive sort-by-key function to SortArray

Problem/Motivation

There are several places in core where we need to sort an array by key, recursively (the recipe system has a usage of this, and a couple of tests do too) -- and there are instances in contrib where it's needed too (see #3550165: DefaultRelativeUrlPropSource does not sort properties keys for comparison, for example).

This would be useful for us to have generically.

Proposed resolution

Add a \Drupal\Component\Utility\SortArray::sortByKeyRecursive() method which does exactly what it says.