Add Ambient Energy to SDFGI

[mrjustaguy]

Describe the project you are working on

Night

Describe the problem or limitation you are having in your project

SDFGI goes full on pitch black which is undesirable.

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

Adding Ambient Energy, separate from the Sky reads it's doing, to allow for adding a minimum amount of light that will illuminate objects even when there is little to no GI light, to avoid having a fully pitch black screen in poorly lit areas

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

Add a new settings to SDFGI:

1. Ambient Color (What color for the energy added to be, default White)
2. Ambient Energy (How much to add, 0 results in current behavior, default probably 0.05, to avoid ever having GI be pitch black)

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

No, attempts to use other methods to give a minimum amount of light such as Reflection Probes failed (SDFGI just got overriden by them)

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

SDFGI is core, and this problem is with it

[Calinou]

Duplicate of godotengine/godot#55104. This is actually a bug.