Exposed path properties save UID if referencing a resource

Currently, if a user or some resource exposes a path in a script,
if this references a resource path it will be saved as a full path.

This will make refactoring not work if the resource pointed towards
changes location or is renamed.

This change makes it so an uid:// path is saved internally in case
a path to a resource has been selected, effectively making it refactor proof.

editor/editor_properties.h

@@ -142,6 +142,8 @@ class EditorPropertyPath : public EditorProperty {
 	LineEdit *path = nullptr;
 	Button *path_edit = nullptr;
 
+	String _get_path_text();
+
 	void _path_selected(const String &p_path);
 	void _path_pressed();
 	void _path_focus_exited();