Used by the constraint solver loop to cache all state for a particle and accumulate solver results. Uses a gather/scatter mechanism to read/write data to the particle SOAs at the beginning/end of the constraint solve. Constraint solver algorithms, and collision Update functions are implemented to use FSolverBody, and do not directly read/write to the particle handles. Constraint Solvers will modify P(), Q(), V() and W() via ApplyTransformDelta() and other methods.