Fixed crash when ESLint rule has multiple rule arguments

[JoshuaKGoldberg]

PR Checklist

• Addresses an existing issue: fixes TypeError: rule.ruleArguments is not iterable #581
• That issue was marked as status: accepting prs

Overview

I could only reproduce #581's crash for an existing .eslintrc.js containing a rule specifying multiple arguments:

"@typescript-eslint/indent": [
    "error",
    4,
    {
        "ignoreComments": false
    }
],

The root issue was that normalizeESLintRules was converting the raw rules into an object with a single value in ruleArguments, not an array:

const [rawRuleSeverity, ruleArguments] =
    configuration instanceof Array ? configuration : [configuration, {}];
const ruleSeverity = normalizeRawESLintRuleSeverity(rawRuleSeverity);

{
  ruleArguments: 4,
  ruleName: '@typescript-eslint/indent',
  ruleSeverity: 'error'
}

If configuration is an array, it should be [configuration[0], configuration.slice(1)] to capture the rule arguments as an array.