Class `SoftConstrainSolidBodyRegion` cannot be used more than once for the same body

[FabienPean-Virtonomy]

https://github.com/Xiangyu-Hu/SPHinXsys/blob/190d0ef53122fb33e0dfb229f56ab0b2980b059d/SPHINXsys/src/shared/particle_dynamics/solid_dynamics/constraint_dynamics.cpp#L255-L264

Registering the variable prevents using several of this type of constraint in a single simulation because it leads to error if it is constructed more than once for the same body:

Error: the variable 'TemporaryVelocity' has already been registered!