Remove insert_or_spawn function family

[ElliottjPierce]

Objective

Based on and closes #18054, this PR builds on #18035 and #18147 to remove:

• Commands::insert_or_spawn_batch
• Entities::alloc_at_without_replacement
• Entities::alloc_at
• entity::AllocAtWithoutReplacement
• World::insert_or_spawn_batch
• World::insert_or_spawn_batch_with_caller

Testing

Just removing unused, deprecated code, so no new tests. Note that as of writing, #18035 is still under testing and review.

Future Work

Per this comment on #18054, there may be additional performance improvements possible to the entity allocator now that alloc_at no longer is supported. At a glance, I don't see anything obvious to improve, but it may be worth further investigation in the future.

Migration Guide

The following deprecated functions have been removed:

• Commands::insert_or_spawn_batch
• World::insert_or_spawn_batch
• World::insert_or_spawn_batch_with_caller

These functions, when used incorrectly, can cause major performance problems and are generally viewed as anti-patterns and foot guns.

Instead of these functions consider doing one of the following:

Option A) Instead of despawing entities and re-spawning them at a particular id, insert the new Disabled component without despawning the entity, and use try_insert_batch or insert_batch and remove Disabled instead of re-spawning it.

Option B) Instead of giving special meaning to an entity id, simply use spawn_batch and ensure entity references are valid when despawning.

[ElliottjPierce]

removed blocked since #18147 is merged.

[Henauxg]

There was a comment from Cart in #18054 saying

If we plan on removing support for this, we should also look into some of the "invalid checks" in Entities. Iirc we added additional checking to support this scenario, and we might be able to simplify / optimize some things. Worth digging up the PRs that introduced those changes.

Did someone have a look, if not we could maybe just track this somewhere ?

[ElliottjPierce]

Did someone have a look, if not we could maybe just track this somewhere ?

Yup! I've rewritten most of the Entities allocator 9 times now lol. I'm picturing building from #18670 (which this is blocking). If we don't do v9, I'll take another look at what we end up with.

Also marking as ready for final since it has two approvals. (I think that's how that's supposed to work.)