C#: Update AST printing to include generated cast (wrapping) expressions and generated ToString calls.

Author: michaelnebel

csharp/ql/lib/semmle/code/csharp/PrintAst.qll

@@ -32,7 +32,9 @@ private predicate shouldPrint(Element e, Location l) {
 }
 
 private predicate isImplicitExpression(ControlFlowElement element) {
-  element.(Expr).isImplicit() and
+  // Include compiler generated cast expressions and `ToString` calls if
+  // they wrap actual source expressions.
+  element.(Expr).stripImplicit().isImplicit() and
   not element instanceof CastExpr and
   not element.(OperatorCall).getTarget() instanceof ImplicitConversionOperator and
   not element instanceof ElementInitializer