Fix JS optional-chained member expression.

Author: Bastiaan Marinus van de Weerd

languages/tree-sitter-stack-graphs-javascript/src/stack-graphs.tsg

@@ -3189,7 +3189,12 @@ inherit .containing_class_value
 ;; ##### Member Expressions
 
 (member_expression
-  (_)@object . (_)@property)@member_expr
+  .
+  (_)@object
+  (_)? ; '?.' `optional_chain` operator
+  (_)@property
+  .
+)@member_expr
 {
 
     node member_push

languages/tree-sitter-stack-graphs-javascript/test/expressions/member_expression.js

@@ -15,4 +15,9 @@ let x = 1;
 // Flow around
 
 /**/ x;
-//   ^ defined: 1
+//   ^ defined: 1
+
+// Optional chain
+
+/**/ x?.foo
+//   ^ defined: 1