Refine the way in which hard-to-donate instructions are handled

An instruction may be hard to donate from one module to another if it uses operand ids that could not be donated.

Currently such instructions are replaced by OpCopyObject instructions that copy a constant of the required result type.

A more refined alternative would be to turn the operand ids that could not be donated into references to some other ids of appropriate type, so that an instruction similar to the original is donated.