feat: add PageProps to $./types

[weebao]

Closes #12726

Added a PageProps type for defining page props using the $props() rune.

<!--- file: page.svelte --->
<script>
	import { PageProps } from './$types';

	let { data }: PageProps = $props();
</script>

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🦋 Changeset detected

Latest commit: a195131

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

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@sveltejs/kit	Major

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[Rich-Harris]

preview: https://svelte-dev-git-preview-kit-12967-svelte.vercel.app/

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