Modify bevy_ecs to support removing archetypes and unregistering components

[alice-i-cecile]

As discussed in bevyengine/rfcs#79 and laid out by @james-j-obrien, Bevy's ECS architecture is not optimized for use in worlds with a very large number of archetypes. Fundamentally:

bevy_ecs currently operates under the assumption that archetype and component ids are dense and strictly increasing.

While this is a blocker for efficient implementation of fragmenting / archetypal relations, it's also worth exploring and fixing in its own right.

There are several steps to this:

• Remove the sparse set in table storage Remove sparse set in Table storage #14928
• Replace the FixedBitSet in Access / FilteredAccess Replace FixedBitSet in Access and FilteredAccess with sorted vectors #16784
• Implement a component index, which tracks the tables and archetypes each ComponentId belongs to as well as the column in that table the id inhabits (if any)
• Query and system caches need to be easier to access.
• Query and system caches must be updated to reflect changes to archetypes
• Create and expose tools for deleting component ids
• Create and expose tools for deleting archetypes

This is a tracking issue: as more related work comes along, please link it here and bother Alice to update this issue description.

[cart]

Might be worth reframing this / renaming it. The "dense and strictly increasing" behavior works great (essentially optimally) with a large number of archetypes, provided they are all being used. This is about adapting Bevy ECS to dataflow where the set of archetypes is constantly changing.

[chescock]

#16885 may also be helpful. It would let us get rid of ArchetypeComponentId, which grows and changes even faster than ArchetypeId itself!