Add pretty_generated option for code fields

[Paul-Bob]

Context

Currently, it’s a common pattern to use format_using alongside update_using to render a prettified version of a code field's content while ensuring valid parsing on update. A typical example involves formatting JSON fields like so:

field :body, as: :code,
  format_using: -> {
    JSON.pretty_generate(JSON.parse(value.to_json))
  },
  update_using: -> {
    JSON.parse(value)
  }

This approach, while effective, introduces redundancy and boilerplate code. To streamline this, we propose adding a first-party pretty_generated option, allowing developers to enable this behavior with a simple flag:

field :body, as: :code, pretty_generated: true

[ObiWanKeoni]

Hi @Paul-Bob 👋
Can I suggest a new JSON field that inherits from code_field and has this option?

Thought being that when we render things like custom_css, pretty_generated would have no (or perhaps disastrous) effects when attempting to pretty generate a json value. I think having a json field would also allow us to infer the language as javascript for syntax highlighting and have conditional rendering if, by chance, an app used a text field instead of JSONB and wanted to render it as pretty JSON.

TL;DR instead of:

field :body, as: :code, pretty_generated: true

maybe

field :body, as: :json, pretty_generated: true

What do you think?