Handle sensitive auto-save or backup remote files (Bug#45245)

Handle sensitive auto-save or backup remote files (Bug#45245)

* doc/misc/tramp.texi (Auto-save and Backup):
Describe tramp-allow-unsafe-temporary-files.
(Ad-hoc multi-hops): Use proper format.

* etc/NEWS: Mention confirmation for writing sensitive auto-save
or backup remote files to the local temporary directory..

* lisp/net/tramp-cache.el (tramp-dump-connection-properties):
Strengthen test.

* lisp/net/tramp.el (tramp-allow-unsafe-temporary-files): New defcustom.
(tramp-handle-find-backup-file-name)
(tramp-handle-make-auto-save-file-name): Don't expose sensible
auto-save or backup files on local temporary directory.  (Bug#45245)

* test/lisp/net/tramp-tests.el (tramp--test-always): New defalias.
(tramp-test10-write-region, tramp-test21-file-links)
(tramp--test--deftest-direct-async-process): Use it.
(tramp-test37-make-auto-save-file-name)
(tramp-test38-find-backup-file-name): Extend tests.