JS: Fix CFG successor edges for parenthesized optional chain bases

When a parenthesized expression is the callee/object of an optional
chain step (e.g. `(null)?.()`), the postVisitChainable method was
writing CFG successor edges FROM the ParenthesizedExpression node.
Since ParenthesizedExpression nodes are now bypassed and have no DB
entry, this caused VALUE_NOT_IN_TYPE errors in the successor relation.

Fix by unwrapping ParenthesizedExpression before writing the successor
edge, so the edge is written from the inner expression instead.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: asgerf

javascript/extractor/src/com/semmle/js/extractor/CFGExtractor.java

@@ -1778,6 +1778,10 @@ private void preVisitChainable(Chainable chainable, Expression base, SuccessorIn
 
     private void postVisitChainable(Chainable chainable, Expression base, boolean optional) {
       if (optional) {
+        // Unwrap parenthesized expressions since they have no DB entry.
+        while (base instanceof ParenthesizedExpression) {
+          base = ((ParenthesizedExpression) base).getExpression();
+        }
         writeSuccessors(base, chainRootSuccessors.get(chainable).getSuccessors(false));
       }
       chainRootSuccessors.remove(chainable);