Use Array for node configuration warnings

Previously, the warnings were passed as a string and delimitation of which were hard coded at each implementation.

scene/gui/container.h

@@ -56,7 +56,7 @@ public:
 
 	void fit_child_in_rect(Control *p_child, const Rect2 &p_rect);
 
-	virtual String get_configuration_warning() const override;
+	TypedArray<String> get_configuration_warnings() const override;
 
 	Container();
 };