Double click on scene tree element to focus currently selected node

In 3D it will focus in the first viewport
Enable double click for trees

tools/editor/plugins/spatial_editor_plugin.h

@@ -253,6 +253,9 @@ public:
 	void set_state(const Dictionary& p_state);
 	Dictionary get_state() const;
 	void reset();
+
+	void focus_selection();
+
 	Viewport *get_viewport_node() { return viewport; }