fix: follow-up formatting in print() for block-level elements

[jycouet]

Follow-up to #17319.

The Fragment visitor in print() only flushed sequences on RegularElement, causing block-level elements (Component, SvelteHead, SvelteBoundary, etc.) to be lumped into the same sequence as adjacent nodes. This broke tools that programmatically manipulate the AST (e.g. sveltejs/cli#915).

The fix flushes before and after all block-level element types, ensuring they get their own sequence and proper line separation.

Before

<svelte:head><title>Page Title</title></svelte:head><div>no space</div>
<Component /><Component />
<Component><span>child</span></Component><div>after component</div>
<svelte:boundary><div>boundary content</div></svelte:boundary><div>after boundary</div>
<!--comment--><div>after comment</div>
<div>before comment</div>
<!--comment-->

{#each items as item}
	<div>{item}</div>
{/each}<div>after each</div>

{@render children()}<div>after render</div>
<div>before render</div>
{@render children()}

After

<svelte:head><title>Page Title</title></svelte:head>
<div>no space</div>
<Component />
<Component />
<Component><span>child</span></Component>
<div>after component</div>
<svelte:boundary><div>boundary content</div></svelte:boundary>
<div>after boundary</div>
<!--comment-->
<div>after comment</div>
<div>before comment</div>
<!--comment-->

{#each items as item}
	<div>{item}</div>
{/each}

<div>after each</div>
{@render children()}
<div>after render</div>
<div>before render</div>
{@render children()}

[changeset-bot]

🦋 Changeset detected

Latest commit: ef6d721

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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svelte	Patch

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[svelte-docs-bot]

Preview: https://svelte-dev-git-preview-svelte-17699-svelte.vercel.app/

[github-actions]

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[Rich-Harris]

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