This PR implements support for recursive CTEs based on @isidentical's design here #462 (comment)

Caveats:

It does not attempt to place safeguards against infinite recursion. That could be implemented as a follow-up PR. It would be great to have some syntax like OPTON (MAXRECURSION 100) to prevent infinite recursion. Since the sql parser crate doesn’t support OPTIONS (MAXRECURSION) I might create a max-recursion parameter to the logical and physical plans that can be inserted manually once the logical plan is produced via SQL as a near-term workaround to protect against infinite recursion. I'll do that in a separate follow-on PR though.

It's slower than it needs to be because of the execution plan inserts coalesce and repartition execution steps within the recursive term. This optimization is solved via this follow-on PR. There is also room to omit gathering of statistics for each execution iteration because setting up statistics on each execution iteration is expensive.

Which issue does this PR close?

Closes #462

Rationale for this change

Datafusion should support recursive CTEs so that it can express calculations that depend on the results of previous iterations.

What changes are included in this PR?

Are these changes tested?

Yes, they're tested via the SQL tests. The SQL tests use CSVs introduced by this PR apache/arrow-testing#93

Are there any user-facing changes?