Objective

• Closes Restore read-only World::iter_entities or provide infallible equivalent #22657

Solution

• Exhumes what was previously deprecated and deleted 🧟. iter_entities() is back as an ergonomic way to non-fallibly iterate through all the entities when you only have immutable World access.
• I didn’t implement iter_entities() on Entities because it seems deliberate from conversation in Add an Entities::iter() method to iterate over all entities when you only have &World #6228 … although I could be convinced otherwise if the conversation is outdated.

Testing

• I exhumed the previous ci test