Merge pull request #12639 from MattiasBuelens/fixElideFallthrough

Fix elided syntax kinds falling through to visitConstructor in TypeScript transformer

src/compiler/transformers/ts.ts

@@ -345,6 +345,7 @@ namespace ts {
 
                 case SyntaxKind.PropertyDeclaration:
                     // TypeScript property declarations are elided.
+                    return undefined;
 
                 case SyntaxKind.Constructor:
                     return visitConstructor(<ConstructorDeclaration>node);