is_ptr cannot be used because it follows the chain of types into the 
type which has the context_handle attribute, which is typically "void *" 
and so causes these context handles to be incorrectly detected as 
context handles. Instead, we can use is_aliaschain_ptr to follow the 
chain of aliases without following pointers and the absence of the 
context_handle attribute indicates that it must be present on a type 
after following a pointer.