GPU: Implement fill VRAM command

src/pse/gpu.h

@@ -113,11 +113,13 @@ protected:
 
   // Rendering commands, returns false if not enough data is provided
   bool HandleRenderCommand();
+  bool HandleFillRectangleCommand();
   bool HandleCopyRectangleCPUToVRAMCommand();
   bool HandleCopyRectangleVRAMToCPUCommand();
 
   // Rendering in the backend
   virtual void UpdateDisplay();
+  virtual void FillVRAM(u32 x, u32 y, u32 width, u32 height, u32 color);
   virtual void UpdateVRAM(u32 x, u32 y, u32 width, u32 height, const void* data);
   virtual void DispatchRenderCommand(RenderCommand rc, u32 num_vertices);
   virtual void FlushRender();