LWRP XR Single Pass Instancing Shadow Fixes

After the LWRP refactor, both directional and local shadows were broken for XR when using Single Pass Instancing.  This commit fixes those issues.

com.unity.render-pipelines.lightweight/LWRP/LightweightForwardRenderer.cs

 
             SetupPerObjectLightIndices(ref cullResults, ref renderingData.lightData);
             RenderTextureDescriptor baseDescriptor = CreateRTDesc(ref renderingData.cameraData);
+            RenderTextureDescriptor shadowDescriptor = baseDescriptor;
+            shadowDescriptor.dimension = TextureDimension.Tex2D;
 
             bool requiresCameraDepth = renderingData.cameraData.requiresDepthTexture;
             bool requiresDepthPrepass = renderingData.shadowData.requiresScreenSpaceShadowResolve ||
 
             if (renderingData.shadowData.renderDirectionalShadows)
             {
-                EnqueuePass(cmd, RenderPassHandles.DirectionalShadows, baseDescriptor);
+                EnqueuePass(cmd, RenderPassHandles.DirectionalShadows, shadowDescriptor);
-                EnqueuePass(cmd, RenderPassHandles.LocalShadows, baseDescriptor);
+                EnqueuePass(cmd, RenderPassHandles.LocalShadows, shadowDescriptor);
 
             bool requiresDepthAttachment = requiresCameraDepth && !requiresDepthPrepass;
             bool requiresColorAttachment = RequiresColorAttachment(ref renderingData.cameraData, baseDescriptor) || requiresDepthAttachment;

com.unity.render-pipelines.lightweight/LWRP/Shaders/LightweightScreenSpaceShadows.shader

         {
             half4  pos      : SV_POSITION;
             half4  texcoord : TEXCOORD0;
-            UNITY_VERTEX_INPUT_INSTANCE_ID
             UNITY_VERTEX_OUTPUT_STEREO
         };
 
             UNITY_SETUP_INSTANCE_ID(i);
-            UNITY_TRANSFER_INSTANCE_ID(i, o);
             UNITY_INITIALIZE_VERTEX_OUTPUT_STEREO(o);
 
             o.pos = TransformObjectToHClip(i.vertex.xyz);
 
         half4 Fragment(Interpolators i) : SV_Target
         {
-            UNITY_SETUP_INSTANCE_ID(i);
             UNITY_SETUP_STEREO_EYE_INDEX_POST_VERTEX(i);
 
 #if defined(UNITY_STEREO_INSTANCING_ENABLED) || defined(UNITY_STEREO_MULTIVIEW_ENABLED)