EEVEE-Next: Use clamped linear spherical harmonic eval

This can produce ringing but it is usually not noticeable
since it is only present in indirect lighting.

source/blender/draw/engines/eevee_next/shaders/eevee_display_probe_grid_frag.glsl

@@ -23,6 +23,6 @@ void main()
   vec3 N = normal_view_to_world(vN);
   vec3 lN = transform_direction(world_to_grid, N);
 
-  vec3 irradiance = spherical_harmonics_evaluate_lambert_non_linear(lN, sh);
+  vec3 irradiance = spherical_harmonics_evaluate_lambert(lN, sh);
   out_color = vec4(irradiance, 0.0);
 }

source/blender/draw/engines/eevee_next/shaders/eevee_lightprobe_eval_lib.glsl

@@ -75,5 +75,5 @@ void lightprobe_eval(ClosureDiffuse diffuse,
 {
   SphericalHarmonicL1 irradiance = lightprobe_irradiance_sample(irradiance_atlas_tx, P);
 
-  out_diffuse += spherical_harmonics_evaluate_lambert_non_linear(diffuse.N, irradiance);
+  out_diffuse += spherical_harmonics_evaluate_lambert(diffuse.N, irradiance);
 }

source/blender/draw/engines/eevee_next/shaders/eevee_spherical_harmonics_lib.glsl

@@ -237,20 +237,20 @@ void spherical_harmonics_L2_rotate(mat3x3 rotation, inout SphericalHarmonicBandL
 vec3 spherical_harmonics_evaluate_lambert(vec3 N, SphericalHarmonicL0 sh)
 {
   vec3 radiance = spherical_harmonics_L0_evaluate(N, sh.L0).rgb;
-  return radiance;
+  return max(vec3(0.0), radiance);
 }
 vec3 spherical_harmonics_evaluate_lambert(vec3 N, SphericalHarmonicL1 sh)
 {
   vec3 radiance = spherical_harmonics_L0_evaluate(N, sh.L0).rgb +
                   spherical_harmonics_L1_evaluate(N, sh.L1).rgb * (2.0 / 3.0);
-  return radiance;
+  return max(vec3(0.0), radiance);
 }
 vec3 spherical_harmonics_evaluate_lambert(vec3 N, SphericalHarmonicL2 sh)
 {
   vec3 radiance = spherical_harmonics_L0_evaluate(N, sh.L0).rgb +
                   spherical_harmonics_L1_evaluate(N, sh.L1).rgb * (2.0 / 3.0) +
                   spherical_harmonics_L2_evaluate(N, sh.L2).rgb * (1.0 / 4.0);
-  return radiance;
+  return max(vec3(0.0), radiance);
 }
 
 /**