Support fingerprint readers in Tramp

Support fingerprint readers in Tramp

* doc/misc/tramp.texi (Frequently Asked Questions): Speak about
fingerprint readers.

* lisp/net/tramp-sh.el (tramp-actions-before-shell):
Use `tramp-fingerprint-prompt-regexp'.

* lisp/net/tramp.el (tramp-wrong-passwd-regexp): Add fingerprint
messages.
(tramp-fingerprint-prompt-regexp, tramp-use-fingerprint):
New defcustoms.
(tramp-action-fingerprint, tramp-action-show-message): New defuns.
(tramp-action-show-and-confirm-message): Start check at (point-min).

* test/lisp/net/tramp-tests.el (tramp-test47-read-fingerprint):
New test.

(cherry picked from commit 3fe787ad4d5894df5b540dbd195128118c949c7c)