[Core] Explicit all input vectors in addDForce

[alxbilger]

addDForce computes the term $df += k \frac{\partial \mathbf{f}}{\partial x} \cdot dx + b \frac{\partial \mathbf{f}}{\partial v} \cdot dx$. To perform this operation, we need $dx$, $x$ and $v$ (the derivatives can depend on $x$ or $v$).

However, the vectors $dx$, $x$ and $v$ couldn't be defined as a parameter of addDForce.

$dx$ was implicitly set to vec_id::read_access::dx through the call of readDx. Now, the vector dx can be defined to something different from vec_id::read_access::dx. For example, look at the trick used here to apply addDForce to v:

sofa/Sofa/framework/Simulation/Core/src/sofa/simulation/MechanicalOperations.cpp

Lines 275 to 288 in 52b9786

	/// Compute the current force delta (given the latest propagated velocity)
	void MechanicalOperations::computeDfV(core::MultiVecDerivId df, bool clear, bool accumulate)
	{
	const core::ConstMultiVecDerivId dx = mparams.dx();
	mparams.setDx(mparams.v());
	setDf(df);
	if (clear)
	{
	executeVisitor( MechanicalResetForceVisitor(&mparams, df, false) );
	//finish();
	}
	executeVisitor( MechanicalComputeDfVisitor(&mparams, df, accumulate) );
	mparams.setDx(dx);
	}

(I'm not even sure it works properly).

It's breaking for classes derived from BaseForceField, if this class overrides addDForce. This should not be a significant impact because in general, force fields overrides the addDForce of an intermediate class, such as ForceField or PairInteractionForceField. It's not breaking for the users of BaseForceField, because the dx, x and v parameters can be omitted. Without them, it routes to the previous behavior. However, this legacy method is deprecated.

This PR is an example to be generalised wherever an implicit vector is used.

Note: usually addForce pre-computes derivatives that can be used in addDForce. Adding x and v in addDForce will allow to check that the x and v used in addDForce does correspond to the x and v used in addForce.

[with-all-tests]

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[alxbilger]

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

[th-skam]

👍 same for the other 2 PRs for me.

[alxbilger]

to do: add x and v to the new signature