The pending changes API endpoint should list individual regions for global template changes

Besides changing this endpoint, is there any other complication we can foresee with breaking the 1:1 relationship between what the UI shows in the pending changes list and what corresponds to an entity? Hopefully, it's no big deal, but just wanting to ask before we go down that road.

@effulgentsia

Rough implementation plan:

• (ideally) Get 📌 Make AutoSaveManager::getAutoSaveKey static Active in
• Add a new method to autosave manager saveGlobalRegion - this just appends the region name to the existing key and label
• Change ApiPreviewController to store one entry per model region instead of in one hunk by calling this new method
• Update ApiPublishAllController to group page template entries in $all_auto_saves and join them before calling the existing code

So whilst the title says 'pending changes api' the actual changes are elsewhere.

#3: 📌 Make AutoSaveManager::getAutoSaveKey static Active already landed Jan 17 :)

Crosspost

Per https://git.drupalcode.org/project/experience_builder/-/merge_requests/5..., I'd like @longwave's thoughts here in particular because it's thanks to him we have docs/adr/0005-Keep-the-front-end-simple.md, and @larowlan's remark reveals that here we're deviating from that.