Further optimization in Tramp's file name decomposition

Further optimization in Tramp's file name decomposition

* lisp/net/tramp.el (tramp-syntax): Recompute all file name
components.  Call `custom-set-variables' after loading.
(tramp-build-prefix-format, tramp-build-prefix-regexp)
(tramp-build-method-regexp)
(tramp-build-postfix-method-format)
(tramp-build-postfix-method-regexp)
(tramp-build-prefix-ipv6-format)
(tramp-build-prefix-ipv6-regexp)
(tramp-build-postfix-ipv6-format)
(tramp-build-postfix-ipv6-regexp)
(tramp-build-postfix-host-format)
(tramp-build-postfix-host-regexp)
(tramp-build-file-name-regexp)
(tramp-build-completion-file-name-regexp): New defuns.
(tramp-prefix-format, tramp-prefix-regexp)
(tramp-method-regexp, tramp-postfix-method-format)
(tramp-postfix-method-regexp, tramp-prefix-ipv6-format)
(tramp-prefix-ipv6-regexp, tramp-postfix-ipv6-format)
(tramp-postfix-ipv6-regexp, tramp-postfix-host-format)
(tramp-postfix-host-regexp)
(tramp-remote-file-name-spec-regexp)
(tramp-file-name-structure, tramp-file-name-regexp)
(tramp-completion-file-name-regexp): Convert defuns into defvars.
(tramp-prefix-regexp-alist)
(tramp-postfix-method-regexp-alist)
(tramp-prefix-ipv6-regexp-alist)
(tramp-postfix-ipv6-regexp-alist)
(tramp-postfix-host-regexp-alist)
(tramp-remote-file-name-spec-regexp-alist): Remove.
(tramp-build-remote-file-name-spec-regexp)
(tramp-build-file-name-structure): Simplify.
(tramp-completion-file-name-regexp-alist): New defconst.
(tramp-tramp-file-p, tramp-dissect-file-name)
(tramp-make-tramp-file-name)
(tramp-completion-make-tramp-file-name)
(tramp-rfn-eshadow-update-overlay-regexp)
(tramp-register-file-name-handlers)
(tramp-completion-handle-file-name-all-completions)
(tramp-completion-dissect-file-name, tramp-clear-passwd):
* lisp/net/tramp-ftp.el (tramp-ftp-file-name-handler):
* lisp/net/tramp-sh.el (tramp-sh-handle-vc-registered)
(tramp-compute-multi-hops): Use variables but functions for
file name components.

* test/lisp/net/tramp-tests.el (tramp-test24-file-name-completion):
Use variables but functions for file name components.