feat!: increase generated tsconfig.json strictness

[danielroe]

🔗 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

This is a remake of #2532, but for main branch... (Just close whichever PR is not relevant.)

This increases strictness for the generated tsconfig.json. The most significant change, I think, is noUncheckedIndexedAccess - feel free to remove if you think this is too much! (But of course it can always be disabled by end user.

📝 Checklist

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