fix: add count aggregation for JSON and OBJ_REF types#2497

shuoweil wants to merge 10 commits intomaingoogleapis/python-bigquery-dataframes:mainfrom

shuowei-anywidgte-persiste-mm-tablegoogleapis/python-bigquery-dataframes:shuowei-anywidgte-persiste-mm-tableCopy head branch name to clipboard