Recently I implemented svelte-draft, which is another way to add complete typescript support to svelte. I rewrote almost all examples in https://svelte.dev/tutorial and the result is repo svelte-draft-tutorial.
The solution is different from others in that it's in language level, instead of writing tools such as preprocessor, svelte-draft itself is implemented in TypeDraft, which is a superset of typescript with built-in support for DSL extension, code transformation and literate programming.
Any feedback is welcome! :)