In particular:
- imgui.cpp : move UpdateInputEvents() higher in NewFrame() to match docking + update RenderMouseCursor() to match.
- imgui_draw.cpp: ImDrawList::_ResetForNewFrame() change from c807192ab
- Backends: SDL2. Add MouseWindowID + change SDL_CaptureMouse() test to match docking branch. Not strictly necessary but aimed at reducing drift because we go on and fork this file.
+ moved responsability of checking valid names to TabBarGetTabName() to simplify both branches.
'#if __has_feature(objc_arc)' was removed as callback gets required reference via ImGui_ImplMetal_GetBackendData() so that weakref is not really needed.
