OARIS — C++ for general_polar_volume_type does not compile

The stand alone C++ mapping for general_polar_volume_type does not compile (at least for v6.4 of OpenSplice). This is because the fields within the union have the same name as as their type (also declared in that namespace). Therefore access functions hide the struct declaration below the point at which they are declared.

Suffix all Shape_Model class names with _type to make unique

Suffix each class name in package Shape_Model with '_type'. This is in accordance with the REG's modelling guidelines and is consistent with the rest of the specification. (Note that general_polar_volume_type already has _type suffix - no change required in that respect).