Factor out some Tramp code

Factor out some Tramp code

* lisp/net/tramp-compat.el (tramp-file-name-handler): Don't declare.

* lisp/net/tramp.el (tramp-skeleton-file-truename)
(tramp-skeleton-handle-make-symbolic-link): New defmacros.
(tramp-handle-file-truename):
* lisp/net/tramp-sh.el (tramp-sh-handle-make-symbolic-link)
(tramp-sh-handle-file-truename):
* lisp/net/tramp-smb.el (tramp-smb-handle-make-symbolic-link):
* lisp/net/tramp-sudoedit.el (tramp-sudoedit-handle-file-truename)
(tramp-sudoedit-handle-make-symbolic-link): Use them.

* lisp/net/tramp.el (tramp-call-process, tramp-call-process-region):
Let-bind `temporary-file-directory'.

* test/lisp/net/tramp-tests.el (tramp-action-yesno):
Suppress run in tests.
(tramp-test21-file-links, tramp-test29-start-file-process)
(tramp-test30-make-process, tramp-test42-utf8): Adapt tests.