docs(vue-virtual): use onUpdated to prevent scroll jumping

[Mini-ghost]

🎯 Changes

• Closes Cannot scroll up in vue dynamic example #619
• Closes Vue: Scroll reset/jump when going up with dynamic height rows #925
• Closes Vue: Scroll stutters/gets stuck when scrolling up #1028

✅ Checklist

• I have followed the steps in the Contributing guide.
• I have tested this code locally with pnpm run test:pr.

🚀 Release Impact

• This change affects published code, and I have generated a changeset.
• This change is docs/CI/dev-only (no release).

[changeset-bot]

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Latest commit: 893ad75

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