Add GPUResourceUsage.Staging for both CPU read/write access

Source/Engine/Graphics/Enums.h

@@ -308,6 +308,17 @@ API_ENUM() enum class GPUResourceUsage
     /// - Any resources read or accessed randomly on host, e.g. CPU-side copy of vertex buffer used as source of transfer, but also used for collision detection.
     /// </remarks>
     StagingReadback = 3,
+
+    /// <summary>
+    /// A resource that supports both read and write from the CPU. 
+    /// This is likely to be the common choice for read-write buffers to transfer data between GPU compute buffers and CPU memory. 
+    /// It usually means CPU (system) memory.
+    /// </summary>
+    /// <remarks>
+    /// Usage:
+    /// - Staging memory to upload to GPU for compute and gather results back after processing.
+    /// </remarks>
+    Staging = 4,
 };
 
 /// <summary>