fix(terrain-blending): transparent terrain (#2550)

(cherry picked from commit 7f95ccc)

Author: InTheBottle

package/Shaders/Lighting.hlsl

@@ -3381,7 +3381,7 @@ PS_OUTPUT main(PS_INPUT input, bool frontFace : SV_IsFrontFace)
 
 	// Stored as 1 - vertexAO so the cleared default (0) means no occlusion
 	// for pixels that do not write to this RT (sky, water, grass, effects).
-	psout.Masks2 = float4(1.0 - vertexAO, 0, 0, 0);
+	psout.Masks2 = float4(1.0 - vertexAO, 0, 0, psout.Diffuse.w);
 
 	float stochasticBlend = (screenNoise * screenNoise) < psout.Diffuse.w ? 1.0 : 0.0;
 	psout.NormalGlossiness.w = stochasticBlend;