support enums and nested constants in match statement

The initial version of the pattern matcher in GDScript does not
allow matching on nested identifiers, only one identifiers available
in the current scope.

With the introduction of enums to GDScript that's a huge missing
feature. This commit makes the parser accept indexed constants and
variables to properly support enums.

modules/gdscript/gd_parser.cpp

@@ -1894,7 +1894,26 @@ GDParser::PatternNode *GDParser::_parse_pattern(bool p_static) {
 				return NULL;
 			}
 
-			if (value->type != Node::TYPE_IDENTIFIER && value->type != Node::TYPE_CONSTANT) {
+			if (value->type == Node::TYPE_OPERATOR) {
+				// Maybe it's SomeEnum.VALUE
+				Node *current_value = value;
+
+				while (current_value->type == Node::TYPE_OPERATOR) {
+					OperatorNode *op_node = static_cast<OperatorNode *>(current_value);
+
+					if (op_node->op != OperatorNode::OP_INDEX_NAMED) {
+						_set_error("Invalid operator in pattern. Only index (`A.B`) is allowed");
+						return NULL;
+					}
+					current_value = op_node->arguments[0];
+				}
+
+				if (current_value->type != Node::TYPE_IDENTIFIER) {
+					_set_error("Only constant expression or variables allowed in a pattern");
+					return NULL;
+				}
+
+			} else if (value->type != Node::TYPE_IDENTIFIER && value->type != Node::TYPE_CONSTANT) {
 				_set_error("Only constant expressions or variables allowed in a pattern");
 				return NULL;
 			}