Improve capacity handling for ColliderSet, RigidBodySet.

[waywardmonkeys]

These allow an application to reduce the cost of reallocation when they know that a large number of colliders or rigid bodies will be created.

[waywardmonkeys]

We may at times create a scene with a large number of colliders and prefer that doing so be fast. (In our case, we're not running physics or rigid bodies. We're also able to disable the colliders as we don't need the full collision detection, just answers to queries.)

For a silly test case of 8,000,000 (200x200x200) things (using many_static.rs as a starter), this reduced the time for populating the sets from 1.3s to 1.0s.

There's a number of questions that could be considered here beyond just these changes:

• Should other sets get this sort of thing?
• Should there be a way to set the capacity for the removed_colliders on ColliderSet?
• Should we give access to methods for capacity, reserve, shrink_to?

[waywardmonkeys]

@Vrixyz @sebcrozet Just checking in on this...

[waywardmonkeys]

Should this point to this PR?

[Vrixyz]

Ideally yes, but it's rare to have the PR link, I'm adding it arbitrarily on bigger/breaking/difficult PRs

[Vrixyz]

I'll merge this as-is ; as for your questions,

Should other sets get this sort of thing?

A good idea.

Should there be a way to set the capacity for the removed_colliders on ColliderSet?

If there's a real use case for it, I'd approve it, but probably pass in the exact values of each properties, so each properties can be tweaked ?

Should we give access to methods for capacity, reserve, shrink_to?

Probably a good idea, but I'd prefer a real use case too.

[waywardmonkeys]

Should we give access to methods for capacity, reserve, shrink_to?

Probably a good idea, but I'd prefer a real use case too.

My concern here is that you add a ton of things, so the storage gets really big, but after that, there's only a few modified per frame, so most of that storage is wasted. This isn't new with my changes, but just thinking about the overall impact of everything in this area...