Also print function data when printing module functions.

Also print function data when printing module functions.

This is especially useful in cases where modules only use a single
entry point and use the data to dispatch to the actual function.  Such
a design is common for languages such as Go and C++.

* src/emacs-module.c (module_function_data): New function.

* src/print.c (print_vectorlike): Use it to print module function data
if not NULL.
(print_object): Adapt size of buffer.

* test/data/emacs-module/mod-test.c (emacs_module_init): Pass some
non-NULL data to ‘mod-test-sum’.
(Fmod_test_sum): Check that correct data is passed through.

* test/src/emacs-module-tests.el (mod-test-sum-test)
(module-function-object): Adapt unit tests.