feat: svelte support

[thenbe]

Description

This PR adds svelte support (as per #282 (comment))

It includes the following rules:

1. Stylistic rules for users not using prettier

2. The recommended rule-set from eslint-plugin-svelte

3. Rules that users always need to amend for svelte anyways, such as:

   • setting varsIgnorePattern for svelte specific stuff such as $$Props
   • turning off import/no-mutable-exports because svelte uses export let myprop to declare props
   • etc

4. Some additional rules from eslint-plugin-svelte that are likely to indicate an issue (I tried to avoid the more opinionated ones)

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Linked Issues

Additional context

A few points:

• The Rules type does not include svelte rules because they are not a part of https://github.com/antfu/eslint-define-config.
• For the dependency setup: Users are only prompted to install eslint-plugin-svelte. They don't need to install svelte-eslint-parser directly, since it's already a dependency of eslint-plugin-svelte.
  • NOTE: I had to include svelte-eslint-parser as a peer dependency. Without it, this project will fail to build (it errors about not finding svelte). And if we install svelte and remove svelte-eslint-parser, we can build but we get an error when consuming this package Error: Dynamic require of "fs" is not supported. This current setup builds successfully and can be consumed successfully.

[antfu]

Thanks! In general I am happy to have it, if you are willing to help maintaining it (like I might ping you when ppl raise Svelte related issues), is that ok for you? Thanks

[antfu]

I wonder how many rules are in it? Should we just expand it inline so have a clear image what to include and compose (for example, would it include some rules in the stylistic category?)

[thenbe]

There are 14 rules marked as recommended today, none of which are categorized as stylistic.

I don't have an opinion on this issue, we can be more explicit by expanding the rules.

[thenbe]

expanded: 9e31d9d (#364)

[thenbe]

Sure thing!