Fix Bug#30946

Fix Bug#30946

* doc/misc/tramp.texi (Multi-hops): Mention host name checks.

* lisp/net/tramp.el (tramp-set-syntax, tramp-dissect-file-name)
(tramp-debug-message, tramp-handle-shell-command):
* lisp/net/tramp-adb.el (tramp-adb-handle-shell-command):
* lisp/net/tramp-archive.el (tramp-archive-file-name-handler)
(tramp-archive-dissect-file-name):
* lisp/net/tramp-gvfs.el (tramp-gvfs-file-name-handler): Adapt callees.

* lisp/net/tramp-compat.el (tramp-compat-user-error): Move defsubst ---

* lisp/net/tramp-sh.el (tramp-compute-multi-hops): Check for proper
host names in multi-hop.  (Bug#30946)

* lisp/net/tramp.el (tramp-user-error): ... here.  Make it a defun.

* test/lisp/net/tramp-tests.el (tramp-test03-file-name-host-rules):
New test.