[DataFusion] Split expressions.rs

[asfimport]

It is now 3k LOC that are largely independent.

Reporter: Jorge Leitão / @jorgecarleitao
Assignee: Jorge Leitão / @jorgecarleitao

PRs and other links:

• GitHub Pull Request #9312

_{Note: This issue was originally created as ARROW-11369. Please see the migration documentation for further details.}

[asfimport]

Jorge Leitão / @jorgecarleitao:
Issue resolved by pull request 9312
#9312