Fixed cull and z test mode, because with blending decal values were blended twice per decal

ScriptableRenderPipeline/HDRenderPipeline/HDRP/Material/Decal/Decal.shader

             Name "DBuffer"  // Name is not used
             Tags { "LightMode" = "DBuffer" } // This will be only for opaque object based on the RenderQueue index
 
-			// need to optimize this and use proper Cull and ZTest modes for cases when decal geometry is clipped by camera 
-            Cull Off
+			// back faces with zfail, for cases when camera is inside the decal volume
+            Cull Front
-			ZTest Always
+			ZTest Greater
 			// using alpha compositing https://developer.nvidia.com/gpugems/GPUGems3/gpugems3_ch23.html
 			Blend SrcAlpha OneMinusSrcAlpha, Zero OneMinusSrcAlpha