[hellopablo]

Summary

• Keep a dragged admin table row from collapsing the table: the placeholder cells hold the row's height, and the drag preview is a table so the clone keeps its column widths.
• Leave list sortables on the existing helper. Only a tbody.js-admin-sortable gets the table-row behaviour.

Test plan

• On a table with two or more tall rows, drag a row and confirm the gap stays the height of the row, stays visible, and moves with the pointer.
• Confirm the other rows do not jump or resize, and the clone keeps the column widths.
• Drop the row and confirm .js-admin-sortable__order is rewritten in the new order.
• Drag a non-table sortable elsewhere in admin and confirm it still behaves as before.