Add backwards compatibly handling of sum stats of extension types #7014

Performance Gate Passed

✅ 1009 untouched benchmarks
⏩ 1515 skipped benchmarks¹

_{Comparing adamg/fix-old-sum-stat-compatability (d090552) with develop (12fe78e)}

1515 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩