add sub screen

Example/SaveSystem/Scene/SaveSystem.tscn

@@ -28,3 +28,8 @@ anchor_right = 1.0
 anchor_bottom = 0.5
 grow_horizontal = 2
 grow_vertical = 2
+
+[node name="Window" type="Window" parent="."]
+mode = 3
+initial_position = 3
+current_screen = 1

project.godot

@@ -20,6 +20,8 @@ config/icon="res://EGFramework.svg"
 
 window/size/viewport_width=1600
 window/size/viewport_height=900
+window/size/mode=3
+window/subwindows/embed_subwindows=false
 
 [dotnet]