Add a LightmapProbe gizmo size editor setting

[Calinou]

• Decrease default size of LightmapProbe gizmos to make smaller-scale scenes with dense probes easier to edit.

cc @lander-vr

Preview

Before

After

After (probe size set to 0.0 in editor settings)

[lander-vr]

Nice! Works as expected. This is a really nice quality of life improvement.

I'm wondering if it'd be feasible to make probe size be based off of the distance towards neighboring probes?

I think it makes sense to have probes that cover a smaller area be smaller, while probes responsible for a larger area be larger, especially as we tackle improved automatic probe spawning behavior in the future.
E.g. imagine a sparse outdoor probe network with a dense indoor probe network, needing to restart the editor and adjust the size is probably not ideal in that scenario.

Another option could be to clamp the scale of the probes as the camera gets nearby, though, while that would be nice (and these suggestions aren't mutually exclusive), I don't think this would be as versatile as having variable probe sizes based on e.g. distance to closest neighboring probe.

[akien-mga]

Thanks!