Feature Request Checklist

• I have pulled the latest main branch of the repository.
• I have searched for related issues and found none that matched my issue.

Overview

Per flint.fyi/rules, Flint is intended to have a unnecessaryUndefinedDefaults rule in the TypeScript plugin (ts). It'll behave roughly equivalently to the existing implementations in other linters to start. This issue tracks adding that rule.

Adding this rule will entail creating the following new source files:

• packages/ts/src/rules/unnecessaryUndefinedDefaults.ts: implementation of the rule itself
• packages/ts/src/rules/unnecessaryUndefinedDefaults.test.ts: tests for the rule
• packages/site/src/content/docs/rules/ts/unnecessaryUndefinedDefaults.mdx: documentation of the rule

Additionally, the following files will need to be edited:

• packages/comparisons/src/data.json: Comparisons data will need to mention the rule is now "status": "implemented"
• packages/ts/src/plugin.ts: Included rules should have the new one inserted in alphabetical order

Additional Info

Existing rules in other linters:

• Biome: noUselessUndefined
• ESLint: unicorn/no-useless-undefined
• Oxlint: unicorn/no-useless-undefined

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