Prevent line-mode term from showing user passwords

Prevent line-mode term from showing user passwords

For buffers whose mode derive from comint-mode, the user password is
read from the minibuffer and it's hidden.  A buffer in term-mode and
line submode, instead shows the passwords.  Make buffers in line
term-mode to hide passwords too (Bug#30190).

* lisp/term.el (term-send-invisible): Prefer the more robust
`read-passwd' instead of `term-read-noecho'.
(term-watch-for-password-prompt): New function.
(term-emulate-terminal): Call it each time we receive non-escape
sequence output.

Co-authored-by: Noam Postavsky <npostavs@gmail.com>