Add sort-keys rule. Fixes #75

[RobertAKARobin]

Prerequisites checklist

• I have read the contributing guidelines.

What is the purpose of this pull request?

Adds a sort-keys rule for JSON that mimics the functionality of the existing sort-keys for JS.

What changes did you make? (Give an overview)

Added a sort-keys rule and tests.

Related Issues

Fixes #75

Is there anything you'd like reviewers to focus on?

I started by copying over the existing code for JS sort-keys, but it required some big modifications in order to work on JSON. It would be nice if there was an automated way to make sure this sort-keys maintains parity with that sort-keys to keep things consistent across ESLint packages, but JS and JSON are different enough that I'm not sure how it could be done.

json/tests/rules/sort-keys.test.js

Line 2 in 7fe2782

* @fileoverview Tests for sort-keys rule. Cribbed from https://github.com/eslint/eslint/blob/main/tests/lib/rules/sort-keys.js. TODO: How to maintain parity with eslint/sort-keys?

Note that I added a TODO for how comments affect line-separated groups

[linux-foundation-easycla]

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• ✅ login: RobertAKARobin / name: Robin (Robert) Thomas (3111b08, f7096a8, 35d8b9a, 541a876, 7ccba2c, d651aae, 2bed7d7)

[RobertAKARobin]

I hate to add a dependency, but since natural-compare is already a dependency of ESLint then I hope this is OK.