[error] Save mlir stderr and add to run_pipeline_with_repro_report error message

[vakumar1]

• currently the run_pipeline_with_repro_report utility captures the python object sys.stderr and adds this output to the error message
• any MLIR errors are written directly to the stderr file descriptor which bypasses this capture
• --> capture the error written to the stderr file descriptor itself (note that there is a limit of 10k chars - this can be modified as needed)