[Draft] Support SvelteJS

[softmarshmallow]

Design to Svelte

Styling

• https://github.com/sveltejs/rfcs/blob/master/text/0008-style-directives.md#motivation
• https://geoffrich.net/posts/style-directives/

Runtime

• https://github.com/sveltejs/svelte-repl (https://github.com/sveltejs/sites/tree/master/packages/repl)
• https://svelte.dev/repl