Remove insert_or_spawn function family

[ElliottjPierce]

Objective

Based on #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.