Add converters / generators to Sprite

Adds the following menu options to the Sprite editor: "Convert to Mesh2D", "Convert to Polygon2D", "Create CollisionPolygon2D Sibling" and "Create LightOccluder2D Sibling"

(cherry picked from commit c218c631f62b154af41238782280dbb9b2e914f8)

editor/plugins/sprite_editor_plugin.h

@@ -41,9 +41,14 @@ class SpriteEditor : public Control {
 	GDCLASS(SpriteEditor, Control);
 
 	enum Menu {
-		MENU_OPTION_CREATE_MESH_2D,
+		MENU_OPTION_CONVERT_TO_MESH_2D,
+		MENU_OPTION_CONVERT_TO_POLYGON_2D,
+		MENU_OPTION_CREATE_COLLISION_POLY_2D,
+		MENU_OPTION_CREATE_LIGHT_OCCLUDER_2D
 	};
 
+	Menu selected_menu_item;
+
 	Sprite *node;
 
 	MenuButton *options;
@@ -55,7 +60,8 @@ class SpriteEditor : public Control {
 	ConfirmationDialog *debug_uv_dialog;
 	Control *debug_uv;
 	Vector<Vector2> uv_lines;
-
+	Vector<Vector<Vector2> > outline_lines;
+	Vector<Vector<Vector2> > computed_outline_lines;
 	Vector<Vector2> computed_vertices;
 	Vector<Vector2> computed_uv;
 	Vector<int> computed_indices;
@@ -71,7 +77,14 @@ class SpriteEditor : public Control {
 
 	void _debug_uv_draw();
 	void _update_mesh_data();
-	void _create_mesh_node();
+
+	void _create_node();
+	void _convert_to_mesh_2d_node();
+	void _convert_to_polygon_2d_node();
+	void _create_collision_polygon_2d_node();
+	void _create_light_occluder_2d_node();
+
+	void _add_as_sibling_or_child(Node2D *p_own_node, Node2D *p_new_node);
 
 protected:
 	void _node_removed(Node *p_node);