bug#50989: 28.0.60; nobreak-char-display in Eldoc buffers

[Augusto Stoffel]

Using the pylsp language server via Eglot, I sometimes get docstrings
with lots of non-breaking spaces in them.  Those end up being
highlighted with the `nobreak-space' face in the Eldoc buffer, which is
very distracting.

I'm not sure this should be addressed in Eglot or in Eldoc.  But the
following advice fixes things for me.
    
    (advice-add 'eldoc--format-doc-buffer :after
                (lambda (&rest _) "Don't display non-breaking spaces."
                  (with-current-buffer eldoc--doc-buffer
                    (setq-local nobreak-char-display nil))))