Provide a way to extend/modify Top Bar Items

This specifically started from 📌 [PP1] Show entity information on the Top Bar Postponed . By default, we'll show title and published/not published for an entity. But if you use content moderation/workspaces, you might want to show the moderation state or thee current workspace or something like that instead. And contrib might want to add more features.

I'm not sure if an alter hook is the answer for that. It's a plugin system, it already comes with a plugin alter hook. content_moderation can alter the default entity info plugin and show the moderation state, it's just a question of how much code we have to duplicate in that plugin.

But such alter hooks, both on the plugin and on render arrays tend to run into conflicts if multiple modules want to change things.

I'd suggest we finish the referenced issue and then have a specific follow-up for content moderation to tie unto that. In core or I'm also open to exploring that in moderation_sidebar, but at least the basic information seems like something that core should provide.

The referenced issues here are now fixed, eg.

📌 Define the 3 areas the Top Bar will provide Active
📌 [PP1] Show entity information on the Top Bar Postponed

We also had a follow up issue to bake in the moderation state if available:

✨ Display content moderation state in the Navigation Top Bar Active

I believe that has resolved the point at issue that inspired this issue. As @berdir pointed out there is some baked in ability in the plugin system to alter / override things.

I'm going to Close this issue for now. If further situations come up that further illustrate the need for some better DX, we can revisit.