Further fixes while testing tramp-crypt

Further fixes while testing tramp-crypt

* doc/misc/tramp.texi (External methods): Remove experimental note
for rclone.
(Keeping files encrypted): Mark file encryption as experimental.

* lisp/net/tramp-adb.el (tramp-adb-file-name-handler-alist):
Use `tramp-handle-file-truename'.
(tramp-adb-handle-file-truename): Remove.

* lisp/net/tramp-crypt.el (tramp-crypt-file-name-handler-alist):
Add `file-writable-p'.
(tramp-crypt-send-command): Return t if no error.
(tramp-crypt-do-encrypt-or-decrypt-file-name)
(tramp-crypt-do-encrypt-or-decrypt-file): Raise an error if it fails.
(tramp-crypt-do-copy-or-rename-file): Flush file properties also
when copying a directory.
(tramp-crypt-handle-file-writable-p): New defun.
(tramp-crypt-handle-insert-directory): Check for library
`text-property-search'.

* lisp/net/tramp-gvfs.el (tramp-gvfs-handle-set-file-uid-gid):
Rename from `tramp-gvfs-set-file-uid-gid'.

* lisp/net/tramp-sh.el (tramp-sh-handle-file-truename):
Use `tramp-handle-file-truename' as fallback.

* lisp/net/tramp.el (tramp-handle-file-truename):
Let-bind `tramp-crypt-enabled' to nil.
(tramp-handle-write-region): Set also file ownership.

* test/lisp/net/tramp-tests.el (tramp-test17-insert-directory):
Skip if needed.