Add support for Svelte

[srikrsna]

What changed / motivation ?

The unplugin doesn't work with Svelte out of the box. This PR adds support for Svelte along with an example of using the unplugin in a sveltekit project.

Pre-flight checklist

• I have read the contributing guidelines
  Contribution Guidelines
• Performed a self-review of my code

[vercel]

@srikrsna is attempting to deploy a commit to the Meta Open Source Team on Vercel.

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[henryqdineen]

I don't see an attrs function in this PR? I'm guessing your lib directory got ignored because of the .gitignore in the root of the repo