ImDrawData: added AddDrawList() helper function. (#6406, #4879, #1878)

imgui.h

@@ -2756,6 +2756,7 @@ struct ImDrawData
     // Functions
     ImDrawData()    { Clear(); }
     IMGUI_API void  Clear();
+    IMGUI_API void  AddDrawList(ImDrawList* draw_list);     // Helper to add an external draw list into an existing ImDrawData.
     IMGUI_API void  DeIndexAllBuffers();                    // Helper to convert all buffers from indexed to non-indexed, in case you cannot render indexed. Note: this is slow and most likely a waste of resources. Always prefer indexed rendering!
     IMGUI_API void  ScaleClipRects(const ImVec2& fb_scale); // Helper to scale the ClipRect field of each ImDrawCmd. Use if your final output buffer is at a different scale than Dear ImGui expects, or if there is a difference between your window resolution and framebuffer resolution.
 };