[6.x] Fix dragging assets onto folders in list view

[jaygeorge]

Description of the Problem

In the asset browser's list view, dropping an asset onto a folder row throws Cannot read properties of undefined (reading 'find') and nothing moves. Grid view works.

What this PR Does

• Table uses this.assets to find the dragged asset but never declared the assets prop, so it was undefined. It's declared now, the same way Grid does it.
• Folder rows were also writing the hovered folder into draggingFolder, the same value that tracks a folder being dragged. Hovering now has its own dragOverFolder, as in Grid.

list-view-folder-drop.mp4

How to Reproduce

1. Go to Assets, switch to list view and open a folder that has a subfolder and some assets.
2. Drag an asset onto the subfolder's row.
3. Nothing moves, and the error shows in the console.