[#811] Fix deriveRPC's call to customGeneric' so that field ordering is maintained

Description

Problem: deriveRPC procedure adds "RPC" prefix to fields for a type to make it RPC counterpart, before passing the new type to customGeneric' function to derive a generic instance for it. The structure of the RPC type and the shape of its generic representation is supposed to be identical to that of the original type. But the suffixing of "RPC" to the fields cause the sorting order to change, customGeneric' function ends up generating wrong methods in the generated Generic instance.

Solution: When the genericStrategy is passed to customGeneric', modify the field ordering functions to strip the "RPC" suffix before applying the sorting logic. This ensures that the field ordering remains the same as how it was in the original type.

Related issue(s)

Resolves: #811 (closed)

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