Add Close/Quit button to Embedded Game Window

[yosimba2000]

This is for Godot 4 Beta 1 .Net

Originally I thought there wasn't a built-in way to close the embedded game window, but there actually is. You just use the buttons on the top right of Godot Editor.

godotengine/godot#101680

My issue is that since there is essentially a pause button for the embedded game window, it also makes sense to add a Stop/Quit button for the embedded game window as well. It's confusing to place the Pause/Suspend and Quit buttons on opposite sides of the Interface.