docs: Link to migration guide from <svelte:component> documentation

[joakim]

It's not obvious how to create dynamically rendered components in Svelte 5.

If you come from Svelte 4 and search for svelte:component, you'll most likely end up on this page, which only gives a cursory explanation for runes mode. The migration guide's section on <svelte:component> has a great example that clears things up. Adding a link to that would be very helpful.

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[Rich-Harris]

preview: https://svelte-dev-git-preview-svelte-14737-svelte.vercel.app/

this is an automated message

[joakim]

Maybe also add a section on dynamically rendered components to Basic markup? For people not used to <svelte:component>.

[Rich-Harris]

thanks!