Svelte 5 rewrite

This would close #9672, assuming we want it. I kind of like it!

This allows snippets to have multiple arguments in the type system. For example, you could type a component expecting a two-argument snippet as:

<script lang="ts">
  let {
    message,
    card
  } = $props<{
    message: string;
    card: Snippet<[message: string, darkMode: boolean]>;
  }>(); 
</script>

{@render card(message, false)}

It would also enable truly variadic snippets:

type MySnippet = Snippet<string[]>;

would be renderable as:

{@render snippet('as', 'many', 'strings', 'as', 'i', 'want')}

Before submitting the PR, please make sure you do the following

• It's really useful if your PR references an issue where it is discussed ahead of time. In many cases, features are absent for a reason. For large changes, please create an RFC: https://github.com/sveltejs/rfcs
• Prefix your PR title with feat:, fix:, chore:, or docs:.
• This message body should clearly illustrate what problems it solves.
• Ideally, include a test that fails without this PR but passes with it.

Tests and linting

• Run the tests with pnpm test and lint the project with pnpm lint