opt: [windows] hide window on start

flutter/windows/runner/win32_window.cpp

@@ -117,7 +117,7 @@ bool Win32Window::CreateAndShow(const std::wstring& title,
   double scale_factor = dpi / 96.0;
 
   HWND window = CreateWindow(
-      window_class, title.c_str(), WS_OVERLAPPEDWINDOW | WS_VISIBLE,
+      window_class, title.c_str(), WS_OVERLAPPEDWINDOW,
       Scale(origin.x, scale_factor), Scale(origin.y, scale_factor),
       Scale(size.width, scale_factor), Scale(size.height, scale_factor),
       nullptr, nullptr, GetModuleHandle(nullptr), this);