Expose ComposedFunction as a public API (#37517)
* document ComposedFunction
* add ComposedFunction to News.md
* Give more descriptive names to the fields of ComposedFunction
* export ComposedFunction
Co-authored-by: Jonas Schulze <jonas.schulze7@t-online.de>
Co-authored-by: Takafumi Arakaki <aka.tkf@gmail.com>
