[Rust][DataFusion] Implement Postgres Length Functions

[asfimport]

To break up the large PR this is just the Postgres length functions

Reporter: Mike Seddon / @seddonm1
Assignee: Mike Seddon / @seddonm1

PRs and other links:

• GitHub Pull Request #9509

_{Note: This issue was originally created as ARROW-11651. Please see the migration documentation for further details.}

[asfimport]

Andrew Lamb / @alamb:
Issue resolved by pull request 9509
#9509