Replace IDL FLE2InsertUpdatePayload with new class of same name that is backed by mc_FLE2InsertUpdatePayload_t via composition. New class will be strongly typed (i.e. return tokens, not ConstDataRange). It can use existing generated IDL code to bootstrap (the IDL header has all the declarations for getters/setters that are needed).

For instance, the new class can have a method

EDCDerivedFromDataToken getEdcDerivedToken()

instead of the original IDL method

ConstDataRange getEdcDerivedToken()