Add extra cull margin to Light3D

[ghostsoft]

Exposes extra cull margin parameters similar to GeometryInstance3D to allow modifying the cull margin. This fixes #105063 in the Compatibility and Mobile renderers by letting the user account for the effect of vertices being lit outside of the light's radius (due to vertex interpolation).

This functionality is already in the base VisualInstance3D class and only needs to be exposed to be of use.

[ghostsoft]

I have no clue why this is somehow failing the doc check on Linux / Editor w / Mono. Do the members have to be in alphabetical order perhaps?

[Calinou]

I have no clue why this is somehow failing the doc check on Linux / Editor w / Mono. Do the members have to be in alphabetical order perhaps?

The CI failure is due to incorrect indentation (use 2 tab characters instead of 8 spaces).

[ghostsoft]

Giving this a polite nudge.

[elvisish]

Will this fix the vertex light culling issues (#105063) on Forward+ Rendering or is it only for Compatibility and Mobile?

[pshaughn]

Will this fix the vertex light culling issues (#105063) on Forward+ Rendering or is it only for Compatibility and Mobile?

Just answering as a bystander, and there might be a subtlety I've missed: by my reading, while it won't fix them, it will provide a step in the direction. Once the cull margin exists at all it could be used in Forward+ when a cone or sphere model is being tested to find lit clusters. (For the sphere, I think just adding the margin to the sphere radius would do it. Growing the cone seems like the tricky part.)