docs: rewrite parser config docs to mainly use flat config

[ota-meshi]

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[baseballyama]

Do we need to care that making confusion for users who cannot yet use flat confog?

[ota-meshi]

Hmm. I personally want Svelte users to use flat configs. That's because I think Svelte users prefer ESM. (Legacy JS config format only supports commonjs.)
Also, if you create eslint.config.js in ESM, you can import svelte.config.js into eslint.config.js.
I expect that in the future if parsers and rules can use svelte.config.js, they will be able to lint better since they will understand how users use Svelte.

[baseballyama]

My suggestion is to put both configs in the README for a while.
If one of the ESLint plugins a user uses does not support flat config, they cannot use flat config, so isn't this something we and Svelte users can control?

[ota-meshi]

My suggestion is to put both configs in the README for a while.

I will do that 👍

[baseballyama]

[ask]

Is it ok to lose this line?

[ota-meshi]

If we limit the explanation to parserOptions, the same explanation can be given for both configs, so we have removed the description specific to the legacy config.

[baseballyama]

[ask]

Can we remove this section?

[ota-meshi]

Since the explanation of eslint.config.js uses the parser object, there is no need to explain it again, so I removed it. I added that feature for support for eslint.config.js.

[baseballyama]

Thank you!