Major version: Pivot language from `_key` to `language` field

sanity-plugin-internationalized-array now stores the language identifier in a dedicated language field instead of using _key for this purpose.

When a field has outdated data a warning banner will render to alert users.

Sanity uses _key internally for array item identity, diffing, and reordering. Storing the language ID there caused issues with:

• Array reordering and diffing in the Studio.
• Portable Text operations that rely on stable keys.
• Copy/paste operations between documents where keys could collide.

Before (v4):

{
  "_key": "en", 
  "_type": "internationalizedArrayStringValue", 
  "value": "hello"
}

After (v5):

{
  "_key": "randomKey",
  "language": "en",
  "_type": "internationalizedArrayStringValue", 
  "value": "hello"
}

Read the full migration guide here.