Fix Bug#28889

Fix Bug#28889

* lisp/net/tramp.el: Change autoload cookie to tramp-autoload cookie.
(tramp-completion-file-name-regexp-default)
(tramp-completion-file-name-handler-alist)
(tramp-completion-file-name-handler): Remove autoload cookie.
(tramp-initial-completion-file-name-regexp): Remove.
(tramp-autoload-file-name-regexp): New defconst.
(tramp-register-autoload-file-name-handlers): Use it.
(with-parsed-tramp-file-name): Adapt docstring.  Compute
`tramp-file-name' slots.  (Bug#28889)