[fix] hydrate correct elements when using @html

[baseballyama]

fixes #7115

After executing this line from Kit, nodes contains (maybe unexpected) #text node at the top and end.

svelte/src/runtime/internal/Component.ts

Line 161 in 03ef0e4

const nodes = children(options.target);

In this case, start_index is more than 0 (mostly 1).
And the second argument of splice is delete_count.
Therefore it will splice more than expected.

svelte/src/runtime/internal/dom.ts

Line 504 in 03ef0e4

const html_tag_nodes = nodes.splice(start_index, end_index + 1);

If start_index is possibly more than 0, I think it should be modified to look like this PR.

On the other hand, should we prevent containing unexpected #text nodes at the top and end?
I think we can not control it because a template file containing %svelte.body% can be freely created by a user.

---

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Tests

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[benmccann]

@hbirler you may be interested in reviewing this hydration fix

[baseballyama]

@tanhauhau

I'm sorry for mentioning it.
But could you please review this PR?
This is just 1 line fix.
And the last committer is you, so I believe you can review it in less time.

[hbirler]

Hi, sorry I did not notice my mention earlier, the fix seems good to me as well.