change on main's abi_def(?) causing native contract unit tests for system contracts to fail compile

[spoonincode]

On main, there is some change in abi_def (or something closely related I didn't track it down) that is causing system contracts' native contract unit tests to fail to compile. See
https://github.com/eosnetworkfoundation/eos-system-contracts/actions/runs/4248437173 for example. Also encountered it on EVM contract. I wouldn't be surprised if many native contract unit tests out in the wild would be ensnared by this.

Depending on the difficulty of getting this abi_def difference resolved, we could also just say it requires everyone downstream to update their test code. If that's the case, need to create issues in eos-system-contracts & reference-contracts.

[heifner]

This was caused by: #696 Specifically the change 62903c0
In the past when we changed abi_serializer we deprecated the methods when we realized it caused this kind of issue. Those methods are still there and deprecated actually. We could do the same thing for set_abi and a constructor that takes by const& instead of by rvalue reference.