fix(sdk.v2): Fix a couple of ParallelFor related bugs. Fixes #6383, fixes #6628

[chensun]

Description of your changes:
Fixes #6383
Fixes #6628

• Fix get get inputs logic for loop arguments.
• Fix "punch the hole" logics for ParallelFor and Condition.
• Clean up some unused code.
• Add test cases reported by the above issues and more.
• Combine test samples: pipeline_with_loop_output.py, pipeline_with_loop_parameter.py, and pipeline_with_loop_static.py into pipeline_with_loops.py

Checklist:

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[ji-yaqi]

/lgtm
/approve

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