Avoid calculating dynamic lights when lights are already baked using the static bake mode in the Forward+ renderer

[clayjohn]

Fixes an issue related to: #85145

When baking a light with the static bake mode, the light is calculated twice. Once when baking and once at runtime. The light values are added together resulting in double lighting.

Shadows are already skipped using the exact same code, but the actual lighting was still being added.

Opening as draft as I need to check the mobile renderer and the compatibility renderer

[Calinou]

For context, there's already a skip in place here for directional lights:

godot/servers/rendering/renderer_rd/shaders/forward_clustered/scene_forward_clustered.glsl

Lines 1853 to 1855 in 694d3c2

	if (directional_lights.data[i].bake_mode == LIGHT_BAKE_STATIC && bool(instances.data[instance_index].flags & INSTANCE_FLAGS_USE_LIGHTMAP)) {
	continue; // Statically baked light and object uses lightmap, skip
	}

It does the job when shadows are enabled, but not when shadows are disabled. This PR fixes double lighting in Forward+ when using a DirectionalLight3D with shadows disabled (although note that its shadows will be baked anyway).

To clarify, the bug I mentioned in #85145 does not occur in Forward+ (neither in 4.3.stable nor master), only in Mobile. To fix #85145, we need to add the same logic used in Forward+ in Mobile (there are no instances of LIGHT_BAKE_STATIC in scene_forward_mobile.glsl currently).

I've tested this PR locally and it fixes double lighting when shadows are disabled on a DirectionalLight3D in Forward+.

[clayjohn]

That other check only disables shadows. The lighting was added in either case.

For the mobile renderer the check shouldn't be in the shader, it should be excluding the light from the light list when pairing with the object so we don't get any overhead from the light at all

[clayjohn]

@Calinou Updated!

In the end this was the situation:

1. Forward+ was missing the check for the light portion (it was only checked for shadows and the flag was only passed in when shadows were enabled)
2. Mobile was missing the check everywhere. The correct space to add it is in the shader for directional lights, but during pairing for positional lights
3. Compatibility did the check for positional lights after pairing, so the check became redundant.

It should be ready to go now!

[Calinou]

Tested locally, it mostly works as expected in all rendering methods. Performance increases as expected when baking with the Static bake mode as opposed to the default Dynamic.

Testing project: test_lightmapgi_mobile.zip

There's one issue where DirectionalLight3D with shadow disabled still applies double lighting, but only in Compatibility:

DirectionalLight3D shadow enabled (Compatibility)

DirectionalLight3D shadow enabled (Compatibility)

OmniLight3D and SpotLight3D don't have this issue in Compatibility.

[clayjohn]

@Calinou Thanks for checking! It turned out that the vertex lighting codepath in the GLES3 shader was missing the check. I added it and removed the static checks for omnilights and spotlights since they weren't necessary anymore.

This should be ready to go now!

[Calinou]

Works great now 🙂

[AThousandShips]

Suggested change

	continue; // Statically baked light and object uses lightmap, skip
	continue; // Statically baked light and object uses lightmap, skip.

[Repiteo]

Thanks!