V4 feedback: Change createMessagesDeclaration to take an array so monorepos can be supported

[felix-quotez]

Is your feature request related to a problem? Please describe.

I love the type-safety that "createMessagesDeclaration" enables(https://v4.next-intl.dev/docs/workflows/typescript#messages-arguments)!

I have multiple packages in a monorepo (two Next.js apps and some shared UI components). The UI package has shared translation messages. When running either of the two Next.js apps, I would like to be able to add the messages of the UI package to createMessagesDeclaration so that an additional .d.ts file will be created.

Describe the solution you'd like

Suggestion:

const withNextIntl = createNextIntlPlugin({
  experimental: {
    createMessagesDeclaration: ['./messages/en.json', '../../packages/ui/messages/en.json'],
  },
})

Describe alternatives you've considered

None yet. (For what it's worth, note that my shared UI package is not bundled or preprocessed in any way because I want to have get hot module reloading. So the two Next.js apps are using the shared code directly.)