Due to virtualization, there are no "row" elements in the data grid anymore.

As the individual cells have a gridcell role, this is causing automated a11y tests to fail: https://developer.mozilla.org/en-US/docs/Web/Accessibility/ARIA/Roles/Gridcell_role

I'm not sure about the right solution:

• should we simply remove the gridcell role?
• should we wrap all of the cells in a single row element (even though it's not 100% correct)?
• Is it possible to introduce dummy elements for rows in the dom tree (AFAIK our virtualization lib doesn't allow this)

cc @myasonik @chandlerprall