Fix command replacement with the Eshell builtin versions of "sudo" and "doas"

Fix command replacement with the Eshell builtin versions of "sudo" and "doas"

This is particularly important when the inner command to execute is an
alias.  Aliases throw 'eshell-replace-command' too, so we want to do
this in two phases: first, replace the "sudo"/"doas" with a
let-binding of 'default-directory', and then later, let the alias code
do its own replacement (bug#68074).

* lisp/eshell/em-tramp.el (eshell/sudo, eshell/doas): Use
'eshell-replace-command' to wrap the inner command.
* test/lisp/eshell/em-tramp-tests.el (mock-eshell-named-command):
Remove.
(em-tramp-test/sudo-basic, em-tramp-test/sudo-user)
(em-tramp-test/doas-basic, em-tramp-test/doas-user): Catch
'eshell-replace-command'.