update slot tutorial content to snippets

[trueadm]

I converted over two tutorial articles to their snippet based equivalent and updated the examples and copy.

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Name	Status	Preview	Comments	Updated (UTC)
omnisite	✅ Ready (Inspect)	Visit Preview	💬 Add feedback	Oct 15, 2024 5:14pm

[Rich-Harris]

I think we're going to need to change how this stuff is taught, because right now it's kinda confusing — the exercise is called 'snippets' but we don't learn what a 'snippet' is until later. We need to begin with the basic concept of snippets and render tags, and work our way up to component composition — we can't just translate the existing content directly. Going to look into this later

[trueadm]

That's a good point. I can take a stab tomorrow on writing up some new tutorials first introducing {#snippet} and then diving into how they're now props and how default snippets and named snippets work based off some of the material I've changed in this PR. If you'd rather do that though, let me know.