docs: refine function usages

[nozomuikuta]

🔗 Linked issue

❓ Type of change

• 📖 Documentation (updates to the documentation, readme, or JSdoc annotations)
• 🐞 Bug fix (a non-breaking change that fixes an issue)
• 👌 Enhancement (improving an existing functionality like performance)
• ✨ New feature (a non-breaking change that adds functionality)
• 🧹 Chore (updates to the build process or auxiliary tools and libraries)
• ⚠️ Breaking change (fix or feature that would cause existing functionality to change)

📚 Description

Resolves #664

As @Barbapapazes suggested, I replace eventHandler calls with defineEventHandler because the latter is more used.
At the same time, I also fixed the following points:

• Sort imports in alphabetical order
  • In this point, it is better to fix docs(examples/from-expressjs-to-h3): add node middleware usage #663 for consistency
• Fix typos
  • Typo fixed by docs: fix import example in 4.event.md #658 is included in this PR too (so, it should be merged first)
• Refine sample codes

📝 Checklist

• I have linked an issue or discussion.
• I have updated the documentation accordingly.

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[pi0]

Thanks ❤️