This would be analogous to std::make_unique/make_shared/make_optional

There would be two overloads - one that takes a variadic pack and forwards it to T's constructor, returning an engaged StatusWith<T>.

The second would take an errorCode and return a disengaged StatusWith<T>.

This would make it possible to write:

return makeStatusWith<StringData>{str, len};

instead of:

return StatusWith<StringData>{StringData{str, len}};

Tack on work: add an of overload uassertStatusOK that takes a StatusWith<T>