R1:686b03a1d59e

Dim the action drop preview element when the cursor approaches

Summary:
Depends on D20308. Ref T5474. The element which previews what will happen when you drop a task somewhere can cover the bottom part of the rightmost column on a workboard.

To fix this, I'm trying to just fade it out if you put your cursor over it. I tried to do this in a simple way previously (":hover" + "opacity: 0.25") but it doesn't actually work because "pointer-events: none" stops ":hover" from working.

Instead, do this in…