Move PackHeightmap/UnpackHeightmap to Common.hlsl.

com.unity.render-pipelines.core/CoreRP/ShaderLibrary/Common.hlsl

 }
 
 // ----------------------------------------------------------------------------
+// Terrain/Brush heightmap encoding/decoding
+// ----------------------------------------------------------------------------
+
+#if defined(SHADER_API_VULKAN) || defined(SHADER_API_GLES) || defined(SHADER_API_GLES3)
+
+float4 PackHeightmap(float height)
+{
+    uint a = (uint)(65535.0f * height);
+    return float4((a >> 0) & 0xFF, (a >> 8) & 0xFF, 0, 0) / 255.0f;
+}
+
+float UnpackHeightmap(float4 height)
+{
+    return (height.r + height.g * 256.0f) / 257.0f; // (255.0f * height.r + 255.0f * 256.0f * height.g) / 65535.0f
+}
+
+#else
+
+float4 PackHeightmap(float height)
+{
+    return float4(height, 0, 0, 0);
+}
+
+float UnpackHeightmap(float4 height)
+{
+    return height.r;
+}
+
+#endif
+
+// ----------------------------------------------------------------------------
 // Misc utilities
 // ----------------------------------------------------------------------------
 

com.unity.render-pipelines.high-definition/HDRP/Material/TerrainLit/TerrainLitDataMeshModification.hlsl

-float UnpackHeightmap(float4 height)
-{
-    // 16-bit height value is packed into two 8-bit channels.
-    return (height.r + height.g * 256.0f) / 257.0f; // (255.0f * height.r + 255.0f * 256.0f * height.g) / 65535.0f
-}
-
 UNITY_INSTANCING_BUFFER_START(Terrain)
     UNITY_DEFINE_INSTANCED_PROP(float4, _TerrainPatchInstanceData)  // float4(xBase, yBase, skipScale, ~)
 UNITY_INSTANCING_BUFFER_END(Terrain)

com.unity.render-pipelines.lightweight/LWRP/ShaderLibrary/Terrain/LightweightPassLitTerrain.hlsl

     float4 _TerrainHeightmapScale;       // float4(hmScale.x, hmScale.y / (float)(kMaxHeight), hmScale.z, 0.0f)
 #endif
 
-float UnpackHeightmap(float4 height)
-{
-    // 16-bit height value is packed into two 8-bit channels.
-    return (height.r + height.g * 256.0f) / 257.0f; // (255.0f * height.r + 255.0f * 256.0f * height.g) / 65535.0f
-}
-
 UNITY_INSTANCING_BUFFER_START(Terrain)
     UNITY_DEFINE_INSTANCED_PROP(float4, _TerrainPatchInstanceData)  // float4(xBase, yBase, skipScale, ~)
 UNITY_INSTANCING_BUFFER_END(Terrain)