Add a secondary light in the Advanced Import Settings preview

[jeronimo-schreyer]

Describe the project you are working on

a 3D Game with small objects and details

Describe the problem or limitation you are having in your project

It's not much, but I want to preview the object with a little more detail

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

I added a secondary light to the preview renderer and UI buttons to turn both lights on and off, just how its done in the materials viewer in the inspector

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

I basically grabbed the code from EditorMaterialPreviewPlugin

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

I think this should be in core

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

This improves the 3D importing experience using the editor

[Calinou]

• See also Tweak environment in the Advanced Import Settings dialog godot#75787.