Request: Use message instead of message_with_string for user visible output?

[T.V. Raman]

Hi,

Emacspeak produces all its spoken feedback via advice --- so in
general, output that gets done purely through the C layer ends up
by-passing the advice layer.

Except in cases where efficiency is the reason for the choice,
could we switch to using message -- instead of
message_with_string to produce output in the echo area that is
 to be seen by the user?

As a place where I'd appreciate a fix, see keyboard.c:

When you press  a key that is currently undefined, the code in
that module uses message_with_string to output a visible "%s is
undefined" message.
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