docs: remove old rollup & sapper, show ts example

[LeoDog896]

• Sapper is deprecated
• Svelte uses Vite to bundle code now
  • The original steps to make svelte-simple-modal work are no longer necessary

[flekschas]

Thanks for the PR. I'm totally fine removing the Sapper instructions and adding the note about TypeScript. However, since Vite uses Rollup under the hood for production bundles, I'm hesitant to remove the Rollup instructions because the deduping might still be something one wants to do.

[LeoDog896]

That makes sense! I've re-added it @flekschas.