Store impulses in contacts and refactor contact data

[Jondolf]

Objective

Having access to contact impulses can be very useful for several tasks, like implementing destructable objects or determining how much damage a hit should deal. Currently, however, this is not really possible.

There should be a way to access contact impulses.

Solution

Add properties for normal and tangent (i.e. friction) impulses to ContactData. These are computed for PenetrationConstraints in the constraint solver and stored in Collisions in the new SubstepSet::StoreImpulses system set.

The impulses can be accessed in Collision events or using the Collisions resource. Note that the impulses in Collision events are currently only from the last substep.

Impulses are stored instead of forces for a few reasons:

• It's more efficient internally, as it skips some operations
• Impulses might make more sense for impacts
• It's what e.g. Box2D and Unity use

Computing the corresponding force is simple however, as you just need to divide by the (substep) delta time. For this, the contact types also have helpers like normal_force and tangent_force.

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Changelog

• Added SubstepSet::StoreImpulses with a store_contact_impulses system
• Added normal and tangent impulses and contact index to ContactData
• Added total normal and tangent impulses to Contacts
• Added manifold index to ContactManifold
• Added collider entities and the contact manifold index to PenetrationConstraint
• Added SingleContact struct, which is used by the contact query
• Removed force properties from PenetrationConstraint in favor of impulses
• Changed contact normal debug rendering to scale based on the impulse by default
  • Added ContactGizmoScale enum for configuring the scaling