Make dbuffer render target clearing code more efficient (also fixes and issue where the 'mask' target wasn't cleared)

ScriptableRenderPipeline/HDRenderPipeline/HDRP/HDRenderPipeline.cs

 				// for alpha compositing, color is cleared to 0, alpha to 1
 				// https://developer.nvidia.com/gpugems/GPUGems3/gpugems3_ch23.html
 
-				Color clearColor = new Color(0.0f, 0.0f, 0.0f, 1.0f);
-				HDUtils.SetRenderTarget(cmd, camera, m_DbufferManager.GetBuffersRTI(), m_CameraDepthStencilBuffer, ClearFlag.Color, clearColor);
+//				Color clearColor = new Color(0.0f, 0.0f, 0.0f, 1.0f);
+//				HDUtils.SetRenderTarget(cmd, camera, m_DbufferManager.GetBuffersRTI(), m_CameraDepthStencilBuffer, ClearFlag.Color, clearColor);
+
+                m_DbufferManager.ClearTargets(cmd, camera);
-				Color clearColorNormal = new Color(0.5f, 0.5f, 0.5f, 1.0f); // for normals 0.5 is neutral
-				m_DbufferManager.ClearNormalTargetAndHTile(cmd, camera, clearColorNormal);
+//				Color clearColorNormal = new Color(0.5f, 0.5f, 0.5f, 1.0f); // for normals 0.5 is neutral
+//				m_DbufferManager.ClearNormalTargetAndHTile(cmd, camera, clearColorNormal);
 
 				HDUtils.SetRenderTarget(cmd, camera, m_DbufferManager.GetBuffersRTI(), m_CameraDepthStencilBuffer); // do not clear anymore
                 m_DbufferManager.SetHTile(m_DbufferManager.bufferCount, cmd);

ScriptableRenderPipeline/HDRenderPipeline/HDRP/Material/Decal/DBufferManager.cs

             RTHandle.Release(m_HTile);
         }
 
+        public void ClearTargets(CommandBuffer cmd, HDCamera camera)
+        {
+            // for alpha compositing, color is cleared to 0, alpha to 1
+            // https://developer.nvidia.com/gpugems/GPUGems3/gpugems3_ch23.html
+
+            Color clearColor = new Color(0.0f, 0.0f, 0.0f, 1.0f);
+            Color clearColorNormal = new Color(0.5f, 0.5f, 0.5f, 1.0f); // for normals 0.5 is neutral
+            HDUtils.SetRenderTarget(cmd, camera, m_RTs[0], ClearFlag.Color, clearColor);
+            HDUtils.SetRenderTarget(cmd, camera, m_RTs[1], ClearFlag.Color, clearColorNormal);
+            HDUtils.SetRenderTarget(cmd, camera, m_RTs[2], ClearFlag.Color, clearColor);
+            HDUtils.SetRenderTarget(cmd, camera, m_HTile, ClearFlag.Color, CoreUtils.clearColorAllBlack);
+        }
+
         public void ClearNormalTargetAndHTile(CommandBuffer cmd, HDCamera camera, Color clearColor)
         {
             // index 1 is normals