Add support for Application.DispatcherShutdownMode property

[lindexi]

What would you like to be added

Add support for Application.DispatcherShutdownMode property.

Why is this needed

Now the default behavior is DispatcherShutdownMode.OnLastWindowClose. After multi window supports, we can create a multi window application. So that we need the DispatcherShutdownMode.OnExplicitShutdown mode.

For which platform

Skia (WPF), Skia (Linux X11), Skia (Linux Framebuffer), Skia (GTK)

Anything else we need to know?

No response

[lindexi]

How can we solve it? We can create an empty window to control the application.

If we need the DispatcherShutdownMode.OnExplicitShutdown mode, we can create an empty window by var controlWindow = new Window();.

Why this hack way can prevent the UNO application exit? Because the last window will be the controlWindow which never be closed.

You can find my demo code in https://github.com/lindexi/lindexi_gd/blob/0a255766f42d373c4c584b7ac1c7cd0dbaed3e95/UnoDemo/DispatcherShutdownMode