feat(Forms): add `preventChangeValidator` to each field

[tujoworker]

Should we even call it "Validator"? It acts very similar and has the same API. But it does also a little more, as it actually prevents the "new value" to be a part of the data set. Something which is not possible with our other validators. But on the other side, it also shows an error. So it "validates" the field. Any thoughts?

Quick example:

<Field.SelectCountry
  label="Land du er statsborger i"
  required
  preventChangeValidator={(value, { connectWithPath }) => {
    const { getValue } = connectWithPath('/countries')
    if ((getValue() || []).includes(value)) {
      return new Error(
        'You can not have the same country twice',
      )
    }
  }}
/>

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Name	Status	Preview	Comments	Updated (UTC)
eufemia	✅ Ready (Inspect)	Visit Preview	💬 Add feedback	Sep 15, 2024 5:29am

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[langz]

I think we should think about this PR:

• What we want to solve
• How we want to solve it

Could/should this be a prop to Iterate.Array, like allowDuplicates or uniqueValue.

Here are two scenarios I quickly came across when testing the newly updated example:

Not being able to submit after removing the duplicate item:

https://github.com/user-attachments/assets/828d80fb-9211-4a19-988a-15b769aa382c

Not being able to submit after changing the duplicate item to be an other country(unique):

https://github.com/user-attachments/assets/46357831-1f5c-42ef-be77-a3dc1cdece89

[tujoworker]

Thank you for the feedback 🫶

I agree, we should not add this validator, because it creates a couple of UX issues you demonstrate, but rather use the validator we have on the Iterate.Array.

This PR #3953 adds a duplication check.