Align on parameter passing style

[westonpace]

The rules we use in Arrow are:

• If a copy of the variable will never be made then pass const T& if the object is deep and T if the object is shallow (note, I find this deep/shallow thing annoying because things that start out shallow can become deep, so I'm open to improvement)
• If a copy of the variable might be made (or will always be made) then pass T to allow the caller to std::move and avoid the copy
• If the variable itself needs to be modified (e.g. an out parameter) then pass T*. This is different than the google C++ style guide which prefers T&. In Arrow, T* is preferred because it makes it obvious the value is being modified at the call site.