Add a test for Iter/ReIter parameters in ParDos (such as after a GBK).

Some bugs popped up recently because DoFn validation caused an error with ParDos that had Iter/ReIter elements. That could've been caught if a test existed that checked the creation of ParDos with Iter/ReIters, so that should be added, either as a new test or as part of some existing integration test.

Imported from Jira [BEAM-9611](https://issues.apache.org/jira/browse/BEAM-9611). Original Jira may contain additional context.
Reported by: danoliveira.

Start by locating the existing integration tests for ParDos and the DoFn validation involved in Iter/ReIter elements. Add coverage for creating a ParDo with Iter/ReIter after a GBK, and consider the work complete when the test catches the validation regression.

Written by the indexing model from the issue text.