ARROW-10559: [Rust][DataFusion] Split up logical_plan/mod.rs into sub…

… modules

The module has gotten fairly large and so refactoring it into smaller chunks will improve readability – as suggested by Jorge apache#8619 (review)

This PR just moves code around -- it is not intended to change any semantics

Reviewing it commit-by-commit might be helpful to see how each piece went

I can also break it up into a sequence of smaller PRs if that would help review

Closes apache#8639 from alamb/alamb/ARROW-10559-split-up

Authored-by: alamb <andrew@nerdnetworks.org>
Signed-off-by: Jorge C. Leitao <jorgecarleitao@gmail.com>