Add 3D editor gizmo icons for Decal, LightmapProbe and FogVolume

[Calinou]

• Tweak CPUParticles3D editor gizmo icon to use the same outline color as other gizmo icons. Make the internal icon easier to see by using an orange color instead of gray.

Lightmap probes that are automatically generated by LightmapGI don't have gizmo icons, as these are not nodes in the first place. Only manually authored LightmapProbe nodes have an icon.

Preview

Left: Decal, middle left: CPUParticles3D, middle right: GPUParticles3D, right: LightmapProbe

FogVolume:

• This closes Vulkan: Decals can't be selected by clicking on them in the 3D editor viewport #57283 and closes LightmapProbes not selectable in the 3D editor viewport #78432, as giving the decals and lightmap probes a gizmo icon makes them selectable by clicking the gizmo icon in the 3D editor viewport. (The same also applies to FogVolume.)

[jcostello]

@Calinou does it make it selectable with box select too?

[Calinou]

@Calinou does it make it selectable with box select too?

Yes 🙂

[YuriSizov]

@MewPurPur You're brilliant! 🚀

[Calinou]

@MewPurPur Thanks a lot! I've added you as a co-author 🙂

[akien-mga]

Thanks!