Fast add/remove components via bit flipping.

[CooCooCaCha]

It's well known that adding/removing components is a slow operation in archetype-based ECS systems. One solution that Unity is working on for their ECS (also archetype-based) is using bit flipping to enable/disable components quickly at runtime.

Here's the CTO of Unity describing their approach:
https://forum.unity.com/threads/dots-skill-system-repo-available.894007/#post-5875804

I imagine something like this could be useful for Bevy.

[alice-i-cecile]

This should be (largely) addressed with the new sparse component storage that we're targeting for 0.5 :)

[alice-i-cecile]

This was added via sparse set components in #1525 :D

[alice-i-cecile]

This was not added in the end, and would be very useful for fast component add / removals. Making another issue for that topic though.

The adds are computationally quick, but do not allow you to insert or remove components within a single stage.