bug#25151: 26.0.50; read-char prompt does not minibuffer face

[Drew Adams <drew.adams@oracle.com>]

This raises a good question.

I guess you are suggesting that face `minibuffer-prompt'
should be used here?  If so, is that face intended to be a
prompt face in general (i.e., THE prompt face, by default)
or just a _minibuffer_ prompt face?

It might make sense for the faces for other kinds of prompt
to look the same, by default, as `minibuffer-prompt'.  (Or
it might not.)

But according to its name, face `minibuffer-prompt' is 
specific to prompting when reading input in the minibuffer.
(And that's not the case for `read-char', `y-or-n-p', etc.)

It could be decided that `minibuffer-prompt' is to be used
for prompting in general.  In that case it really should be
called something like `prompt'.

But I think it would make more sense to create a separate
face `prompt', and (perhaps) let `minibuffer-prompt' inherit
from it.

Some users might, in particular, want to see a difference
when they are prompted and reading is NOT from the minibuffer.
Functions that read characters without using the minibuffer
can confuse users, and a difference in prompt face could give
them an idea that input is being read differently.

Recently Emacs Dev decided to just add face `minibuffer-prompt'
to the prompt for `y-or-n-p'.  I'd sooner see a separate face
be used for non-minibuffer input prompting (even if the default
appearance might be the same).