The list defining the common storage types was defined in
DefaultTypes.h.in. The problem was that derived default types could not
just add their own type. They had to redefine the whole list.
Instead, move the list to StorageList.h. Also updated
DefaultTypesVTK.h.in to use this list when using XGC. This enables
ArrayHandleSOA for this case.
Previously, the PolicyDefault used to compile all the filters was hard-
coded. The problem was that if any external project that depends on VTK-
m needs a different policy, it had to recompile everything in its own
translation units with a custom policy.
This change allows an external project provide a simple header file that
changes the type lists used in the default policy. That allows VTK-m to
compile the filters exactly as specified by the external project.
