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.