Validation of `list:true` fields - missing indexes

[adrians5j]

Currently, for list: true fields, we just iterate over values, and if a value is invalid, we throw an error and stop the process.

And even more importantly, the error that is thrown, doesn't tell on which index in the list the error occurred, just the field name.

In previous version, we had the exact index, so let's try to bring that back.