Support multi-cell copy/paste in result set and spreadsheet editors

A potential customer is evaluating DoltHub. They like the spreadsheet-based UI in DoltHub and think it could be a good UI for the non-developer users at their company who are tasked with updating/inserting data and reviewing data changes. For example, in one table, these users would like to select and copy several rows in the table at the same time, then copy them into new rows, edit the row values, and then submit the changes.