fix: follow-up formatting in `print()` for block-level elements (#17699)

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](https://github.com/sveltejs/cli/pull/915)).

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

### Before

```svelte
<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
<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/print-block-element-separation.md

@@ -0,0 +1,5 @@
+---
+"svelte": patch
+---
+
+fix: follow-up formatting in `print()` — flush block-level elements into separate sequences

packages/svelte/src/compiler/print/index.js

@@ -371,9 +371,23 @@ const svelte_visitors = {
 					}
 				}
 			} else {
+				const is_block_element =
+					child_node.type === 'RegularElement' ||
+					child_node.type === 'Component' ||
+					child_node.type === 'SvelteHead' ||
+					child_node.type === 'SvelteFragment' ||
+					child_node.type === 'SvelteBoundary' ||
+					child_node.type === 'SvelteDocument' ||
+					child_node.type === 'SvelteSelf' ||
+					child_node.type === 'SvelteWindow' ||
+					child_node.type === 'SvelteComponent' ||
+					child_node.type === 'SvelteElement' ||
+					child_node.type === 'SlotElement' ||
+					child_node.type === 'TitleElement';
+
+				if (is_block_element && sequence.length > 0) flush();
 				sequence.push(child_node);
-
-				if (child_node.type === 'RegularElement') flush();
+				if (is_block_element) flush();
 			}
 		}
 

packages/svelte/tests/print/samples/block-element-separation/input.svelte

@@ -0,0 +1,25 @@
+<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()}
+
+<Component />   <div>with spaces</div>
+<Component><span>child</span></Component>   <div>spaces after component</div>
+<!--comment-->   <div>spaces after comment</div>
+{@render children()}   <div>spaces after render</div>
+
+<Component />
+<div>newline between</div>
+<!--comment-->
+<div>newline after comment</div>
+{#each items as item}
+<div>{item}</div>
+{/each}
+<div>newline after each</div>
+{@render children()}
+<div>after render</div>

packages/svelte/tests/print/samples/block-element-separation/output.svelte

@@ -0,0 +1,42 @@
+<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()}
+<Component />
+<div>with spaces</div>
+<Component><span>child</span></Component>
+<div>spaces after component</div>
+<!--comment-->
+<div>spaces after comment</div>
+{@render children()}
+<div>spaces after render</div>
+<Component />
+<div>newline between</div>
+<!--comment-->
+<div>newline after comment</div>
+
+{#each items as item}
+	<div>{item}</div>
+{/each}
+
+<div>newline after each</div>
+{@render children()}
+<div>after render</div>