Tramp: Support different proxies for the same destination

Tramp: Support different proxies for the same destination

* doc/misc/tramp.texi (Ad-hoc multi-hops): New subsection "Using
different proxies for the same destination".

* etc/NEWS: Tramp supports different proxies for the same
destination host name in parallel.
Fix typos.

* lisp/net/tramp-cmds.el (tramp-cleanup-connection): Fix docstring.

* lisp/net/tramp.el (tramp-make-tramp-file-name): Don't call
`tramp-add-hops' during file name completion.
(tramp-handle-file-name-as-directory)
(tramp-handle-file-name-directory): Use `tramp-cache-undefined'
for an empty `tramp-default-proxies-alist'.
(tramp-add-hops): Extend.  Remove existing entries with same
target and different proxy, if needed.  (Bug#74219)

(cherry picked from commit 6cde51f1bbcfd55fe8d189b045247b9d80dee4ea)