Create Screenspace texture macro for LWRP

This handles declarations between Tex2D and Tex2DArray.  The latter is used for Stereo Instancing.

ScriptableRenderPipeline/LightweightPipeline/LWRP/ShaderLibrary/Core.hlsl

     ApplyFogColor(color, unity_FogColor.rgb, fogFactor);
 }
 
+
+#if defined(UNITY_STEREO_INSTANCING_ENABLED) || defined(UNITY_STEREO_MULTIVIEW_ENABLED)
+    #define SCREENSPACE_TEXTURE TEXTURE2D_ARRAY
+#else
+    #define SCREENSPACE_TEXTURE TEXTURE2D
+#endif // defined(UNITY_STEREO_INSTANCING_ENABLED) || defined(UNITY_STEREO_MULTIVIEW_ENABLED)
+
 #endif

ScriptableRenderPipeline/LightweightPipeline/LWRP/ShaderLibrary/InputBuiltin.hlsl

     return M;
 }
 
+// Move these to Core.hlsl
 #if defined(UNITY_SINGLE_PASS_STEREO)
 float2 TransformStereoScreenSpaceTex(float2 uv, float w)
 {

ScriptableRenderPipeline/LightweightPipeline/LWRP/ShaderLibrary/Shadows.hlsl

 
 #include "CoreRP/ShaderLibrary/Common.hlsl"
 #include "CoreRP/ShaderLibrary/Shadow/ShadowSamplingTent.hlsl"
+#include "Core.hlsl"
-#if defined(UNITY_STEREO_INSTANCING_ENABLED) || defined(UNITY_STEREO_MULTIVIEW_ENABLED)
-TEXTURE2D_ARRAY(_ScreenSpaceShadowMap);
-#else
-TEXTURE2D(_ScreenSpaceShadowMap);
-#endif
+SCREENSPACE_TEXTURE(_ScreenSpaceShadowMap);
 SAMPLER(sampler_ScreenSpaceShadowMap);
 
 TEXTURE2D_SHADOW(_ShadowMap);

ScriptableRenderPipeline/LightweightPipeline/LWRP/Shaders/LightweightScreenSpaceShadows.shader

         #include "LWRP/ShaderLibrary/Core.hlsl"
         #include "LWRP/ShaderLibrary/Shadows.hlsl"
 
-#if defined(UNITY_STEREO_INSTANCING_ENABLED) || defined(UNITY_STEREO_MULTIVIEW_ENABLED)
-        TEXTURE2D_ARRAY(_CameraDepthTexture);
+        SCREENSPACE_TEXTURE(_CameraDepthTexture);
-#else
-        TEXTURE2D(_CameraDepthTexture);
-        SAMPLER(sampler_CameraDepthTexture);
-#endif
 
         struct VertexInput
         {