Fix HDRP warnings on 2020.X (#260)

* Fix HDRP warnings on 2020.2

* Updating changelog

* Fixing HDRP version expression on 2019.4

com.unity.perception/CHANGELOG.md

 
 ### Fixed
 
+Fixed compiler warnings in projects with HDRP on 2020.1 and later
+
 ## [0.8.0-preview.2] - 2021-03-15
 
 ### Upgrade Notes

com.unity.perception/Runtime/GroundTruth/RenderPasses/HdrpPasses/GroundTruthPass.cs

             targetDepthBuffer = TargetBuffer.Custom;
         }
 
-        protected sealed override void Execute(
-            ScriptableRenderContext renderContext, CommandBuffer cmd, HDCamera hdCamera, CullingResults cullingResult)
+        //overrides obsolete member in HDRP on 2020.1+. Re-address when removing 2019.4 support or the API is dropped
+#if HDRP_9_OR_NEWER
+        protected override void Execute(CustomPassContext ctx)
+        {
+            ScriptableRenderContext renderContext = ctx.renderContext;
+            var cmd = ctx.cmd;
+            var hdCamera = ctx.hdCamera;
+            var cullingResult = ctx.cullingResults;
+#else
+        protected override void Execute(ScriptableRenderContext renderContext, CommandBuffer cmd, HDCamera hdCamera, CullingResults cullingResult)
+#endif
             // CustomPasses are executed for each camera. We only want to run for the target camera
             if (hdCamera.camera != targetCamera)
                 return;

com.unity.perception/Runtime/GroundTruth/RenderPasses/HdrpPasses/InstanceSegmentationPass.cs

         [UsedImplicitly]
         public InstanceSegmentationPass() {}
 
+        //overrides obsolete member in HDRP on 2020.1+. Re-address when removing 2019.4 support or the API is dropped
+#if HDRP_9_OR_NEWER
+        protected override void Execute(CustomPassContext ctx)
+        {
+            ScriptableRenderContext renderContext = ctx.renderContext;
+            var cmd = ctx.cmd;
+            var hdCamera = ctx.hdCamera;
+            var cullingResult = ctx.cullingResults;
+#else
+#endif
             CoreUtils.SetRenderTarget(cmd, targetTexture, ClearFlag.All);
             m_InstanceSegmentationCrossPipelinePass.Execute(renderContext, cmd, hdCamera.camera, cullingResult);
         }

com.unity.perception/Runtime/GroundTruth/RenderPasses/HdrpPasses/LensDistortionPass.cs

             lensDistortionCrossPipelinePass.Setup();
         }
 
+        //overrides obsolete member in HDRP on 2020.1+. Re-address when removing 2019.4 support or the API is dropped
+#if HDRP_9_OR_NEWER
+        protected override void Execute(CustomPassContext ctx)
+        {
+            ScriptableRenderContext renderContext = ctx.renderContext;
+            var cmd = ctx.cmd;
+            var hdCamera = ctx.hdCamera;
+            var cullingResult = ctx.cullingResults;
+#else
+#endif
             CoreUtils.SetRenderTarget(cmd, targetTexture);
             lensDistortionCrossPipelinePass.Execute(renderContext, cmd, hdCamera.camera, cullingResult);
         }

com.unity.perception/Runtime/GroundTruth/RenderPasses/HdrpPasses/SemanticSegmentationPass.cs

             m_SemanticSegmentationCrossPipelinePass.Setup();
         }
 
+        //overrides obsolete member in HDRP on 2020.1+. Re-address when removing 2019.4 support or the API is dropped
+#if HDRP_9_OR_NEWER
+        protected override void Execute(CustomPassContext ctx)
+        {
+            ScriptableRenderContext renderContext = ctx.renderContext;
+            var cmd = ctx.cmd;
+            var hdCamera = ctx.hdCamera;
+            var cullingResult = ctx.cullingResults;
+#else
+#endif
             CoreUtils.SetRenderTarget(cmd, targetTexture);
             m_SemanticSegmentationCrossPipelinePass.Execute(renderContext, cmd, hdCamera.camera, cullingResult);
         }

com.unity.perception/Runtime/Unity.Perception.Runtime.asmdef

             "name": "com.unity.simulation.capture",
             "expression": "0.0.10-preview.16",
             "define": "SIMULATION_CAPTURE_0_0_10_PREVIEW_16_OR_NEWER"
+        },
+        {
+            "name": "com.unity.render-pipelines.high-definition",
+            "expression": "9.0",
+            "define": "HDRP_9_OR_NEWER"
-}
+}