Rename duplicate column names in read_json(orient='split')
- [X] xref #47718

All our read methods drop duplicated columns (`read_xml` and `read_json(orient='records')`) or rename them with the pattern `x`, `x.1`, `x.2`... (`read_csv`, `read_fwf`, `read_excel`, `read_html`). There is only one exception where the built `DataFrame` contains duplicated columns, which is `read_json(orient='split')`.

Making `read_json(orient='split')` be consistent with the other methods, and rename the duplicate columns here.

Follow ups:

- Use the `dedup_names` function everywhere when columns are renamed #50371
- Add a parameter to the `read_*` functions where the format can have duplicates, to allow better control of the behavior when dealing with duplicate column names #47718

CC: @MarcoGorelli 
Thanks @datapythonista (failures unrelated). Follow up PRs can be submitted if needed