Add facility to make module functions interactive (Bug#23486).

Add facility to make module functions interactive (Bug#23486).

* src/module-env-28.h: Add field for 'make_interactive' function.

* src/emacs-module.c (Lisp_Module_Function): Add new field holding the
interactive form.
(allocate_module_function): Adapt to structure layout change.
(module_make_interactive, module_function_interactive_form): New
functions.
(initialize_environment): Use them.

* src/eval.c (Fcommandp):
* src/data.c (Finteractive_form): Also handle interactive module
functions.

* test/data/emacs-module/mod-test.c (Fmod_test_identity): New test
function.
(emacs_module_init): Create two interactive module test functions.

* test/src/emacs-module-tests.el (module/interactive/return-t)
(module/interactive/return-t-int, module/interactive/identity):
New unit tests.

* doc/lispref/internals.texi (Module Functions): Document new
function.  Rework paragraph about wrapping module functions, as the
example no longer applies.

* etc/NEWS: Document new facility.