Highlight the hovered item in the editor's tree widgets (scene, filesystem, etc.)

[mieldepoche]

Describe the project you are working on

prototypes

Describe the problem or limitation you are having in your project

I stumbled upon a bug I can't reproduce, but it's actually (maybe) a cool thing:

simplescreenrecorder-2023-06-26_09.53.36.webm

(in this video, I am simply moving the mouse over the tree without pressing any button)

As you can see the highlight is always on for some reason (it's supposed to only be there when drag and dropping something in the tree).

Having this full time in the Scene and FileSystem docks would provide a clear indication of which is the hovered row when they are wide (so you're sure) (in my case, this would prove a bit useful for the FileSystem dock -- I widened the scene dock for the sake of the above demonstration, but my FileSystem dock has a similar size on my setup).

A potential drawback is that it looks a bit odd, maybe? And noisy? idk.

Describe the feature / enhancement and how it helps to overcome the problem or limitation

implement this full time

Describe how your proposal will work, with code, pseudo-code, mock-ups, and/or diagrams

like it works now when drag and dropping something

If this enhancement will not be used often, can it be worked around with a few lines of script?

small ux tweak

Is there a reason why this should be core and not an add-on in the asset library?

small ux tweak

[Calinou]

This requires implementing support for hover highlights in Tree, which may be an expensive operation in complex trees (such as the scene tree dock when you have hundreds of nodes).

That said, this should improve usability quite a lot.

cc @davthedev