Restore order of split names in dataset_info for canonical datasets
After a bulk edit of canonical datasets to create the YAML `dataset_info` metadata, the split names were accidentally sorted alphabetically. See for example:
- https://huggingface.co/datasets/bc2gm_corpus/commit/2384629484401ecf4bb77cd808816719c424e57c

Note that this order is the one appearing in the preview of the datasets.

I'm making a bulk edit to align the order of the splits appearing in the metadata info with the order appearing in the loading script.

Related to:
- #5202