Eng 6090 subquery test and fix

For review -- please focus on ee and planner changes -- but do not merge yet:
  I still need to remove some debug prints in the ee
  I may have additional tuning to sqlcoverage input templates
  I need to test for the passing (vs. regressions or incompatibility) of the existing jenkins sqlcoverage scripts
  I need to verify SQLCommand parser changes with SQLCommand test cases.
  I need to implement webstudio parser changes.