[8.x] Add a method to sort keys in a collection using a callback

[redelschaap]

New attempt for this feature, since I really think this offers more flexibility for sorting collection items by key that would otherwise need an unnecessary amount of code. See also PR #40341.

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Other than sorting collection item keys case insensitive, use cases would be:

• Sorting items where keys represent written dates (using a userland function)
• Sorting items where keys represent software versions (using collect([...])->sortKeysUsing('version_compare');)