feat: add Svelte template

[Gugustinette]

Could be based on rollup-plugin-svelte.

[elecmonkey]

I’ve created a template for a Svelte component using rollup-plugin-svelte. However, this plugin only bundles JavaScript and doesn’t produce .d.ts files. Vue leverages rolldown-plugin-dts, which has built-in support for generating Vue type declarations (actually uses vue-tsc internally).

Svelte community provides svelte2tsx, which can output component .d.ts files. So I think we can just include a simple script in the template that invokes svelte2tsx directly to generate type definitions. Maybe it might make sense to maintain the script as a independent npm package.

In the future, we could also consider whether @sxzz would be interested in integrating more built-in capabilities into rolldown-plugin-dts? I’d really appreciate any suggestions from you — thanks a lot!

[sxzz]

I'm not sure if sveltejs/language-tools#2242 will actually move forward in the Svelte community.

At the moment, I don't fully understand how Svelte generates dts files, but I'm open to accepting the PR.