HDRenderPipeline: Fix PI issue in disney Diffuse integration for diffuse

- Fix undesired division by PI for Disney diffuse integration for
diffuse GI
- Add debug constant value HDRI textures
- Change format of DFG integration texture from fp16 to fp11:11:10

Assets/ScriptableRenderPipeline/HDRenderPipeline/Material/Lit/Lit.cs

             {
                 m_InitPreFGD = Utilities.CreateEngineMaterial("Hidden/HDRenderPipeline/PreIntegratedFGD");
 
-                // TODO: switch to RGBA64 when it becomes available.
-                m_PreIntegratedFGD = new RenderTexture(128, 128, 0, RenderTextureFormat.ARGBHalf, RenderTextureReadWrite.Linear);
+                // Value for DisneyDiffuse integration are slightly above one (1.05)
+                m_PreIntegratedFGD = new RenderTexture(128, 128, 0, RenderTextureFormat.RGB111110Float, RenderTextureReadWrite.Linear);
                 m_PreIntegratedFGD.filterMode = FilterMode.Bilinear;
                 m_PreIntegratedFGD.wrapMode = TextureWrapMode.Clamp;
                 m_PreIntegratedFGD.hideFlags = HideFlags.DontSave;

Assets/ScriptableRenderPipeline/ShaderLibrary/ImageBasedLighting.hlsl

         {
             float3 H = normalize(L + V);
             float LdotH = dot(L, H);
-            float disneyDiffuse = DisneyDiffuse(NdotV, NdotL, LdotH, RoughnessToPerceptualRoughness(roughness));
+            float disneyDiffuse = DisneyDiffuseNoPI(NdotV, NdotL, LdotH, RoughnessToPerceptualRoughness(roughness));
 
             acc.z += disneyDiffuse * weightOverPdf;
         }

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