Fix terrain outline by tagging the terrain as opaque (otherwise the output alpha channel from terrain shader is tested and clipped).

ScriptableRenderPipeline/HDRenderPipeline/HDRP/Material/TerrainLit/TerrainLit.shader

     SubShader
     {
         // This tags allow to use the shader replacement features
-        Tags{ "RenderPipeline" = "HDRenderPipeline" "RenderType" = "HDLitShader" "SplatCount"="8" }
+        Tags{ "RenderPipeline" = "HDRenderPipeline" "RenderType" = "Opaque" "SplatCount"="8" }
 
         // Caution: The outline selection in the editor use the vertex shader/hull/domain shader of the first pass declare. So it should not bethe  meta pass.
         Pass

ScriptableRenderPipeline/HDRenderPipeline/HDRP/Material/TerrainLit/TerrainLitSplatCommon.hlsl

     {                                                                                                   \
         albedo[i] = float4(0, 0, 0, 0);                                                                 \
         normal[i] = float3(0, 0, 0);                                                                    \
-        masks[i] = float4(-1, 0, 0, 0);                            \
+        masks[i] = float4(-1, 0, 0, 0);                                                                 \
     }
 
     float2 dxuv = ddx(uv);

ScriptableRenderPipeline/HDRenderPipeline/HDRP/Material/TerrainLit/TerrainLit_Basemap.shader

     SubShader
     {
         // This tags allow to use the shader replacement features
-        Tags{ "RenderPipeline" = "HDRenderPipeline" "RenderType" = "HDLitShader" }
+        Tags{ "RenderPipeline" = "HDRenderPipeline" "RenderType" = "Opaque" }
 
         // Caution: The outline selection in the editor use the vertex shader/hull/domain shader of the first pass declare. So it should not bethe  meta pass.
         Pass