Stabilize `useExtracted`

[amannn]

With next-intl@4.5, there's now experimental support for useExtracted.

The next phase will be to collect feedback, fix bugs, potentially incorporate changes and fill in the gaps for missing features and docs.

TODO

• Fuzzy comments not supported by .po parser (smth else as well?) (ref: there's 1.0 now)
• Wiped out target locales (ref), Investigate and fix translation file emptying bug #2112
• Use en for localeCompare everywhere
• Translations not added (ref)
• Custom formatters for use cases:
  • PO with source as ID
  • Auto-population for pseudo locale
  • Custom JSON
• Rename "formatter" to something like "adapter" or "persist" or "codec" to avoid a naming conflict with useFormatter
• Docs/demo for monorepos (ref)
  • Not shared messages (transpilePackages: ['@acme/ui'] can be used, but not necessarily)
  • Shared messages (what if consumers build messages themselves after running extraction script?)
• More docs for array-esque data (ref)
• Docs about static analyzability
  • Calls to t (ref, related to above point)
  • No wrapping (ref)
  • We should also mention this for useTranslations. It works, but this has downsides (ref)
• Double check PPR works for .po loader
• SWC plugins are "experimental"
• Autocomplete with type augmentation, but allow new messages (ref)
• We should mention in docs that messages are read during build (this might be non-obvious).
• Ask for more feedback
  • Node.js website team

Future explorations

• How to migrate from hand-crafted keys to autogenerated ones (Codemod?)
• A way to migrate catalogs when changing the format
• Tool calls for get all missing translations / translate missing / etc.
• A way to fix source text, i.e. pick a message by key and migrate it to a new message that is synced back into source code (e.g. with an editor, or could we also just watch the source catalog and automatically sync to source?)
• Validation that extracted message for source locale matches source code
• ESLint rule that checks that you're not using dynamic expressions with t
• Provide supplemental descriptions for translations automatically via AI (related: Crowdin Context Harvester)
• Conversion of ID-based projects? (contributions welcome)
• Improve/add defaults
  • Detect srcPath automatically (like Tailwind)
  • Also all others could have defaults, but the question remains whether extraction remains opt-in
• Rust-only version?

This list acts as my personal todo list that I want to share for transparency, but please be sure to comment here if you have feedback for the feature:

→ #2036