feat(module)!: generate withNuxt function for easer composition

[antfu]

This PR makes .nuxt/eslint.config.mjs export a function withNuxt instead of the plan config array. This provides auto-type declaration for users and makes the compositions with other presets easier. It also makes the config factory async in case we later need to dynamic load some modules on conditions.

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[DamianGlowala]

What do you think about defineEslintConfig((nuxt) => [ ... ]) for most flexibility in terms of ordering (also, got used to the defineEslintConfig naming and thinking whether withNuxt would be a better one)?

[antfu]

I did make this

eslint/packages/eslint-config/src/flat/index.ts

Lines 12 to 22 in 35cd711

	/**
	* Provide type definitions for constructing ESLint flat config items.
	*
	* This function takes flat config item, or an array of them as rest arguments.
	* It also automatically resolves the promise if the config item is a promise.
	*/
	export async function defineFlatConfigs(...configs: Awaitable<FlatConfig | FlatConfig[]>[]): Promise<FlatConfig[]> {
	const resolved = await Promise.all(configs)
	return resolved.flat()
	}

and mentioned this

eslint/docs/content/1.packages/1.config.md

Lines 85 to 97 in 35cd711

	To make it easier, you can also use our helper `defineFlatConfigs`, which will also resolve and flatten the configs for you:
	```js [eslint.config.mjs]
	import { defineFlatConfigs, createConfigForNuxt } from '@nuxt/eslint-config/flat'
	export default defineFlatConfigs(
	createConfigForNuxt({
	// options here
	}),
	// other configs
	)
	```

But I think withNuxt would be easier for most of the users and most of time the order of configure don't usually matter as the user configure comes later with higher priority to override stuff.