Changed window reference

[Tkko]

I've changed reference of window object as it is recommended in windows docs.

window.dart
/// Please try to avoid statically referencing this and instead use a
/// binding for dependency resolution such as WidgetsBinding.instance.window.

binding.dart
/// Each of these other bindings could individually access a [Window] statically,
/// but that would preclude the ability to test these behaviors with a fake
/// window for verification purposes. Therefore, [BindingBase] exposes this
/// [Window] for use by other bindings. A subclass of [BindingBase], such as
/// [TestWidgetsFlutterBinding], can override this accessor to return a
/// different [Window] implementation, such as a [TestWindow].

[lizhuoyuan]

beta:

I changed it:

    var mediaQuery = WidgetsBinding.instance?.window ?? ui.window;