Initializes the entity's physics object as a physics shadow. Removes the previous physics object if successful. This is used internally for the Player's and NPC's physics object, and certain HL2 entities such as the crane.

A physics shadow can be used to have static entities that never move by setting both arguments to false.

The created physics object will depend on the entity's solidity SOLID_NONE will not create a physics object, SOLID_BBOX will create a Axis-Aligned BBox one, SOLID_OBB will create Orientated Bounding Box one, and anything else will use the models' physics mesh.