Backends: SDL3: secondary viewports SDL_WindowFlags only inherit SDL_WINDOW_HIGH_PIXEL_DENSITY from the main window. (#8098, #2306)

Amend a526ff8c (#6146)

backends/imgui_impl_sdl3.cpp

@@ -949,9 +949,9 @@ static void ImGui_ImplSDL3_CreateWindow(ImGuiViewport* viewport)
         SDL_GL_MakeCurrent(main_viewport_data->Window, main_viewport_data->GLContext);
     }
 
-    Uint32 sdl_flags = 0;
+    SDL_WindowFlags sdl_flags = 0;
     sdl_flags |= use_opengl ? SDL_WINDOW_OPENGL : (bd->UseVulkan ? SDL_WINDOW_VULKAN : 0);
-    sdl_flags |= SDL_GetWindowFlags(bd->Window);
+    sdl_flags |= SDL_GetWindowFlags(bd->Window) & SDL_WINDOW_HIGH_PIXEL_DENSITY;
     sdl_flags |= (viewport->Flags & ImGuiViewportFlags_NoDecoration) ? SDL_WINDOW_BORDERLESS : 0;
     sdl_flags |= (viewport->Flags & ImGuiViewportFlags_NoDecoration) ? 0 : SDL_WINDOW_RESIZABLE;
     sdl_flags |= (viewport->Flags & ImGuiViewportFlags_NoTaskBarIcon) ? SDL_WINDOW_UTILITY : 0;