fix(Form)!: include nested state in submit data

[romhml]

🔗 Linked issue

#2889

❓ Type of change

• 📖 Documentation (updates to the documentation or readme)
• 🐞 Bug fix (a non-breaking change that fixes an issue)
• 👌 Enhancement (improving an existing functionality)
• ✨ 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

Fixes an issue with nested form state not being included in the @submit event payload.
The proposed solution requires to apply schema transformation to the state (partially reverting #2701) to return the props.state object in the submit event data.

Another alternative would be to return a list of objects in the submit payload (with transformation applied) instead of the full object. We can't easily reconstruct the full object since we don't have the information of a nested form's state path within the parent form's state.

I added a new transform options in the form's validate function to control when transformations are applied. It's currently done on submit only.

📝 Checklist

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

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