Field input error handling behaviours

## Summary

Currently when exceeding field input character limits further text is allowed to be input, but also a warning appears when reaching the limit rather than when exceeding it.

## 💬 Description

Need to establish reasoning behind original design choices for field input error handling and whether these are the best approaches to take.

## 💰 Use value
Clearer implementation for users and better end user experience.

## 📝 Acceptance Criteria
If relevant, describe in full detail the different interactions and edge cases that the component or patterns needs to fulfil.

_Given_
_When_
_Then_

- Identify current implementation.
- Research best practice.
- Decide on action. Create further ticket if necessary.

## ✏ Designs
If there's a Figma design file (or other mock-up), include it here.

## 🧾 Guidance
If there's written guidance or documentation, include a link to it here.

## Additional info

See internal communications for further context.

Start by identifying the current field input implementation and reviewing its existing character-limit and warning behavior. Check the internal communications referenced in the issue and compare the behavior with relevant best practices; done means agreeing on an action and creating a follow-up ticket if implementation work is needed.

Written by the indexing model from the issue text.