Ensure PxSomeFlag::Enum is passed correctly

[PathogenDavid]

PxFlags are translated as [Flags]-style C# enums. This works perfectly for the most part, but there are some places in PhysX where the underlying enum type is referenced directly. (IE: Referring to PxSomeFlag::Enum instead of the PxFlags<PxSomeFlag::Enum, PxU8> type.)

This could be problematic when sizeof(PxFlags<PxSomeFlag::Enum, PxU8>) != sizeof(PxSomeFlag::Enum) (which is generally always when the second template argument isn't 32 bits.) In theory the enum values will always just go into a register anyway, but I need to double check this doesn't cause subtle issues.

It may be easier to just leave this issue to MochiLibraries/Biohazrd#32 since it probably depends on the target platform (and maybe even the target compiler.)

Can [MarshalAs] be used to coerce the enum in these scenarios?