Add automated empty values sanitization

[fzaninotto]

Problem

All form inputs have an empty value of '' (empty string). React-hook-form doesn't sanitize these values by default. This leads to unexpected create and update payloads like:

{
  id: 123,
  title: '',
  author: '',
}

The currently documented solution is to use parse on individual inputs, and/or transform at the controller level.

But none of these solutions is particularly convenient when developers have to use them everywhere. The input-level solution is super repetitive, and the controller-one is at the wrong level - the problem is caused by the form, it should be handled by the form.

Solution

Introduce an opt-in <Form sanitizeEmtyValues> prop

  <Edit>
    <SimpleForm sanitizeEmptyValues>
      <TextInput source="title" />
    </SimpleForm>
  </Edit>
);

Todo

• Create an empty value sanitizer and test it
• Add the support for sanitizeEmptyValues in , , and ``
• Document the new prop
• Remove advice to use transform to sanitize empty values
• In Reference inputs, sanitize empty values by default

[WiXSL]

Can you rebase to include #8162?
We may have to change the note in the docs of AutocompleteInput and SelectInput regarding emptyValue prop being null

[fzaninotto]

Back to WIP as this makes #7782 more pregnant

[fzaninotto]

Back to RFR - we'll fix #7782 in a bug fix release, no need to delay the next minor.