RigidBodyFactory is right between RigidBodyFromResource and
RigidBodyFromShape functions, and some Factory functions are known
to be in the same TU as RigidBodyFromShape functions.
Some factory functions also use FromShape non-static member functions.
Turns out we already have a bunch of ShapeParam classes in
physShapeParam and parts of RigidBody/Shape are just
duplicates -- whoops.
ShapeParam is renamed to ShapeParamObj to avoid any confusion
with the (.*)ShapeParam classes.
Léo Lam