Add remote processes to Tramp sshfs method

Add remote processes to Tramp sshfs method

* doc/misc/tramp.texi (FUSE setup): Method sshfs supports also
remote processes.

* lisp/net/tramp-cache.el (tramp-get-file-property)
(tramp-set-file-property): Move setting of
`tramp-cache-unload-hook' out of function.

* lisp/net/tramp.el (tramp-expand-args): New defun.
(tramp-handle-make-process):
* lisp/net/tramp-sh.el (tramp-do-copy-or-rename-file-out-of-band)
(tramp-maybe-open-connection):
* lisp/net/tramp-sshfs.el (tramp-sshfs-maybe-open-connection):
* lisp/net/tramp-sudoedit.el (tramp-sudoedit-send-command): Use it.

* lisp/net/tramp-sshfs.el (tramp-methods) <sshfs>:
Adapt `tramp-mount-args'.  Add `tramp-login-args',
`tramp-direct-async', `tramp-remote-shell',
`tramp-remote-shell-login' and `tramp-remote-shell-args'.
(tramp-connection-properties): Set "direct-async-process" fir sshfs.
(tramp-sshfs-file-name-handler-alist): Add `exec-path',
`make-process', `process-file', `set-file-modes', `shell-command',
`start-file-process', `tramp-get-remote-gid',
`tramp-get-remote-uid' and `tramp-set-file-uid-gid'.
(tramp-sshfs-handle-exec-path, tramp-sshfs-handle-process-file)
(tramp-sshfs-handle-set-file-modes): New defuns.

* test/lisp/net/tramp-tests.el (tramp-test20-file-modes)
(tramp-test28-process-file, tramp-test29-start-file-process)
(tramp-test30-make-process, tramp-test32-shell-command)
(tramp-test32-shell-command-dont-erase-buffer)
(tramp-test34-explicit-shell-file-name, tramp-test35-exec-path)
(tramp-test43-asynchronous-requests): Run also for tramp-sshfs.
(tramp--test-shell-file-name): New defun.
(tramp-test28-process-file)
(tramp-test34-explicit-shell-file-name)
(tramp-test43-asynchronous-requests): Use it.
(tramp-test40-special-characters-with-stat)
(tramp-test40-special-characters-with-perl)
(tramp-test40-special-characters-with-ls)
(tramp-test41-utf8-with-stat, tramp-test41-utf8-with-perl)
(tramp-test41-utf8-with-ls): Remove superfluous skip.