Add stereo instancing/multi-view support to LWRP mat shaders

ScriptableRenderPipeline/LightweightPipeline/LWRP/ShaderLibrary/LightweightPassLit.hlsl

 
     float4 clipPos                  : SV_POSITION;
     UNITY_VERTEX_INPUT_INSTANCE_ID
+    UNITY_VERTEX_OUTPUT_STEREO
 };
 
 void InitializeInputData(LightweightVertexOutput IN, half3 normalTS, out InputData inputData)
 
     UNITY_SETUP_INSTANCE_ID(v);
     UNITY_TRANSFER_INSTANCE_ID(v, o);
+    UNITY_INITIALIZE_VERTEX_OUTPUT_STEREO(o);
 
     o.uv = TRANSFORM_TEX(v.texcoord, _MainTex);
 

ScriptableRenderPipeline/LightweightPipeline/LWRP/Shaders/LightweightStandardUnlit.shader

                 float4 vertex : SV_POSITION;
 
                 UNITY_VERTEX_INPUT_INSTANCE_ID
+                UNITY_VERTEX_OUTPUT_STEREO
             };
 
             VertexOutput vert(VertexInput v)
                 UNITY_SETUP_INSTANCE_ID(v);
                 UNITY_TRANSFER_INSTANCE_ID(v, o);
+                UNITY_INITIALIZE_VERTEX_OUTPUT_STEREO(o);
                 
                 o.vertex = TransformObjectToHClip(v.vertex.xyz);
                 o.uv0AndFogCoord.xy = TRANSFORM_TEX(v.uv, _MainTex);