GDScript: Support % in shorthand for get_node

The `%` is used in scene unique nodes. Now `%` can also be used instead
of `$` for the shorthand, besides being allowed generally anywhere in
the path as the prefix for a node name.

modules/gdscript/gdscript_parser.h

@@ -749,8 +749,10 @@ public:
 	};
 
 	struct GetNodeNode : public ExpressionNode {
-		LiteralNode *string = nullptr;
-		Vector<IdentifierNode *> chain;
+		String full_path;
+#ifdef DEBUG_ENABLED
+		bool use_dollar = true;
+#endif
 
 		GetNodeNode() {
 			type = GET_NODE;