REF: BinGrouper indices #52468
Description
Ref: #51414 (comment)
In #51414, BinGrouper.__iter__ was changed because the indices in BinGrouper did not behave in the same way that they do for BaseGrouper. I'm guessing (but not sure) it would be better to refactor BinGrouper.indices to better align with those in BaseGrouper. Further investigations in this regard are welcome.