Rather than continuing to use ICON_TEMP, meant to represent temporary locations, this PR adds a specific one - ICON_PREVIEW_LOADING - for this purpose. Just a copy of ICON_TEMP for now, but with all parts at 40% opacity, matching how we use it now. Not only gives us an icon we can later change, but also removes our special handling of reducing opacity for one icon id. Pull Request: https://projects.blender.org/blender/blender/pulls/135463