Move definition of Lisp_Module_Function to emacs-module.c.

Move definition of Lisp_Module_Function to emacs-module.c.

* src/lisp.h: Remove include of emacs-module.h.  Remove definition
of Lisp_Module_Function structure.

* src/emacs-module.c (module_function_documentation)
(module_function_address): New accessor functions for module function
fields.
(emacs_subr, struct Lisp_Module_Function): Move from lisp.h.

* src/print.c (print_vectorlike):
* src/doc.c (Fdocumentation): Use the new accessor functions.