IO: added ImGuiPlatformIO::ClearPlatformHandlers(), ClearRendererHandlers(). Backends: call those on Shutdown(). (#8945, #2769)

imgui.h

@@ -3970,6 +3970,13 @@ struct ImGuiPlatformIO
     // Textures list (the list is updated by calling ImGui::EndFrame or ImGui::Render)
     // The ImGui_ImplXXXX_RenderDrawData() function of each backend generally access this via ImDrawData::Textures which points to this. The array is available here mostly because backends will want to destroy textures on shutdown.
     ImVector<ImTextureData*>        Textures;           // List of textures used by Dear ImGui (most often 1) + contents of external texture list is automatically appended into this.
+
+    //------------------------------------------------------------------
+    // Functions
+    //------------------------------------------------------------------
+
+    void    ClearPlatformHandlers();    // Clear all Platform_XXX fields. Typically called on Platform Backend shutdown.
+    void    ClearRendererHandlers();    // Clear all Renderer_XXX fields. Typically called on Renderer Backend shutdown.
 };
 
 // (Optional) Support for IME (Input Method Editor) via the platform_io.Platform_SetImeDataFn() function. Handler is called during EndFrame().