Make snapshot tests resiliant to Stylelint internal changes

[romaricpascal]

What

Ignore private properties returned by resolveConfig in the snapshot tests and make the ordering of keys stable.

Note

Stylelint has a omitPrivateProperties utility to ignore private properties when stringifying config to JSON for printing with --print-config in the CLI

Why

Snapshot tests keep an eye on the config created by our own rules and those of the config we extend. They run Stylelint's resolveConfig, which returns not only the public list of rules and plugins, but also private properties used internally by Stylelint.

These tests shouldn't break if Stylelint decides to update how it functions internally, so we should be resilient to changes in private properties and ordering of the keys in the generated config.

Done when

• Snapshot ignores Stylelint's private properties in the config and use a consistent order for the keys