> This adds the (internal) Wrapper class, and the Using function that uses it. Given
> a class F that implements Ser(stream, const object&) and Unser(stream, object&)
> functions, this permits writing e.g. READWRITE(Using<F>(object)).
This is a backport of Core PR17896 [1/3]
https://github.com/bitcoin/bitcoin/pull/17896/commits/ca62563df341786d1d1809a037d8b592924e78c4