[C++] Refactor Substrait ToProto/FromProto to visitor pattern

[asfimport]

Currently, the conversion between Acero and Substrait plans is done ad hoc using various overloads of the ToProto and FromProto functions. Code quality may benefit from refactoring this to a visitor pattern, to make it more easy to track state (ExtensionSet), store conversion options, maybe make multiple implementations in the future via inheritance, etc.

It's probably better to do this sooner rather than later (if we're going to do it).

Reporter: Jeroen van Straten / @jvanstraten

_{Note: This issue was originally created as ARROW-16987. Please see the migration documentation for further details.}