Add missing index.ts files to user projects (#39163)

This makes the language service treat .js files inside node_modules as
part of the parent project, so that you can view the same errors in the
editor as you see in the baselines.

Also update a comment in the parser that I missed in an earlier PR.

src/compiler/parser.ts

@@ -3527,7 +3527,7 @@ namespace ts {
                         type = finishNode(factory.createJSDocNonNullableType(type), pos);
                         break;
                     case SyntaxKind.QuestionToken:
-                        // If not in JSDoc and next token is start of a type we have a conditional type
+                        // If next token is start of a type we have a conditional type
                         if (lookAhead(nextTokenIsStartOfType)) {
                             return type;
                         }