Add Commands::insert_batch for faster component modification

[alice-i-cecile]

What problem does this solve or what need does it fill?

Inserting components one at a time is slow.

What solution would you like?

Add Commands::insert_batch and remove_batch to modify components en-masse in a more efficient way.

As discussed in #3227 (comment), this should be a safe, typed equivalent to EntityWorldMut::insert_by_ids that's exposed to commands.

I think that a builder API that iteratively modifies the underlying Command struct is probably the correct design.

What alternative(s) have you considered?

We could use insert_or_spawn_batch for the insertion case, but that does not fail in the desired ways at all.

Additional context

Follows up on the work from #2673, which added insert_or_spawn_batch. Ideally we can use the same strategy for this work, and perform similar benchmarks.

[alice-i-cecile]

We should also include despawn_batch as part of this PR (or in an immediate follow-up PR) for performance reasons.

[cart]

I don't think despawn_batch would meaningfully benefit from batching. Removing arbitrary entities is random-access (even if you somehow managed to sort by archetype, the internal swap remove would still be random). And the recent Commands rework ensures that we reuse allocations. In fact, despawn(a), despawn(b), ... would be faster than despawn_batch(![a, b, ...]) because we could reuse the command allocations across frames, whereas the Vec would need to be allocated each frame.