Is your feature request related to a problem or challenge?

One thing I noticed while working on #9913 with @peter-toth is that keeping track of all the LogicalPlan tree node walking / rewriting is somewhat hard for me (and datafusion/expr/src/logical_plan/plan.rs is getting pretty large).

Describe the solution you'd like

I would like to move all all the code into a single module where we could:

1. Find it more easily
2. Document the overall treenode walking / rewriting situation

Describe alternatives you've considered

(maybe alongside the impl TreeNode for LogicalPlan) ? Maybe somethign like datafusion/expr/src/logical_plan/tree_node.rs or datafusion/expr/src/logical_plan/apply_visit.rs 🤔

Additional context

See also #9913 (comment)