Make the transmission tint an HDR color

Motivation:
- transmission is modulated by the albedo, which controls reflectance, not transmittance
- we do not model specular transmission, so the resulting intensity is lower

ScriptableRenderPipeline/HDRenderPipeline/HDRP/Material/DiffusionProfile/DiffusionProfileSettings.cs

 
         [ColorUsage(false, true)]
         public Color            scatteringDistance;         // Per color channel (no meaningful units)
-        [ColorUsage(false)]
+        [ColorUsage(false, true)]
         public Color            transmissionTint;           // Color, 0 to 1
         public TexturingMode    texturingMode;
         public TransmissionMode transmissionMode;