Provide new `defalias-fset-function' symbol property.

Provide new `defalias-fset-function' symbol property.
* src/lisp.h (AUTOLOADP): New macro.
* src/eval.c (Fautoload): Don't attach to loadhist, call Fdefalias instead.
* src/data.c (Ffset): Remove special ad-advice-info handling.
(Fdefalias): Handle autoload definitions and new Qdefalias_fset_function.
(Fsubr_arity): CSE.
(Finteractive_form): Simplify.
(Fquo): Don't insist on having at least 2 arguments.
(Qdefalias_fset_function): New var.
* lisp/emacs-lisp/advice.el (ad-set-advice-info): Set defalias-fset-function.
(ad--defalias-fset): New function.
(ad-safe-fset): Remove.
(ad-make-freeze-definition): Use cl-letf*.