[TypeScript] Add missing parameter to add function type of <SimpleFormIteratorContextValue>

[Aikain]

Fix #10355

Problem

Wrong add-function type.

Solution

Add missing parameter.

There seems to be no mention in the documentation that a function can be given a parameter. However, I'm not able to produce good enough English to put it in the documentation so I didn't try to add it.

Additional Checks

• The PR targets master for a bugfix, or next for a feature
• The PR includes unit tests (if not possible, describe why) (This is just change of type)
• The PR includes one or several stories (if not possible, describe why) (This is just change of type)
• The documentation is up to date

[slax57]

Thanks!