auto-unwrapping versions of `unwrap_and_` functions

There need to be "auto-unwrapping" versions of `unwrap_and_` functions. That is, when the callable argument returns `result`, the overall result should be that type (or I guess, it should have the same value type, and the error type that is a combination of the error types of the arguments and the error type of the result of `f`).

Below is an example of me using it to implement a custom conversion from to `boost::json::value` to a container type. Container conversion provided by Boost.JSON have a similar structure.

https://godbolt.org/z/74MsK345d