C++ FFI templates

[mantielero]

Yeah. The `Array::Type` is an enum. I got it like: 
    
    
    type
      Type* {.size:sizeof(cuint),header: "Array", importcpp: 
"osg::Array::Type".} = enum
        ## The type of data stored in this array.
        
        ArrayType = 0,
        ByteArrayType = 1,
        ShortArrayType = 2,
        IntArrayType = 3,
        UByteArrayType = 4,
        ....
    
    
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