[feature request] drag a row of the table to the El tree tree node, and the drop event cannot be triggered

### Existing Component
是

### Component Name
el-tree el-table

### Description
将table表格某一行向el-tree 树形节点上拖拽，不能触发drop 事件 . 树形上的允许拖拽已启用 。 且：:allow-drag="()=>{return false}" :allow-drop="()=>{return true}"

Start by reproducing the reported drag from an el-table row onto an el-tree node with the stated allow-drag and allow-drop settings. Trace the drag-and-drop handling for both components and verify whether the tree's drop event is reached. Done means the cross-component drop reliably triggers the expected event.

Written by the indexing model from the issue text.