[SofaGeneralMeshCollision] Direct SAP is written as a narrow phase

[alxbilger]

SAP is usually a method to discriminate pairs of objects that are not in collision. The output is pairs of objects to be further investigated in the narrow phase.
However, in SOFA, the DirectSAP component is written as a component doing the broad phase and the narrow phase. Almost all the work is actually done in the narrow phase. That is why, we can consider this component is mainly a narrow phase component.
All the broad phase code has been removed. It is still a broad phase, but the code is located in its base class: BruteForceBroadPhase.
The narrow phase code has been extracted and put in a new component: DirectSAPNarrowPhase. DirectSAP inherits from DirectSAPNarrowPhase.
In the narrow phase, the result of the broad phase is used to skip the boxes which have been totally ignored in the broad phase. Initially, the DirectSAP component did not perform any discrimination in its broad phase. Now it performs a BruteForceBroadPhase. It is not yet clear if it is always a good choice regarding the performances. In the case of the caduceus scene, the performances are slightly better. I guess if the broad phase takes a lot of time (many objects), it is better to avoid it. DirectSAP would not be the best choice. I would use a more performant broad phase, or no broad phase, when used with DirectSAPNarrowPhase.

From now, the user can decide to design its scene with two different ways resulting to the same behavior:

<DirectSAP/>

or

<BruteForceBroadPhase/>
<DirectSAPNarrowPhase/>

In the second option, it will be possible to change the combination of broad phase/narrow phase.
Note: I kept the component DirectSAP, but I don't think its name is meaningful.

This is the following of the work started in #2010

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[alxbilger]

[ci-build][with-all-tests]

[hugtalbot]

by the way @alxbilger it would be great if you feel it's necessary to update the associated pages (DirectSAP, IncrSAP, BruteForce)