bug#31921: 26.1.50; Add a convenient way to get flymake error at point

[Carlos Pita <carlosjosepita@gmail.com>]

>> So feel free to close this, but please add something wrt this in the
>> docstring or the info manual.
>
> In that case, it's better not to close it.  I've already read this
> complaint/request elsewhere.

I don't know if `C-h .` was intended by design or is the result of
serendipity but it feels like the right solution to me, not as a
workaround or hack. It literally reads as "help at point" and shows
the content of a standard property meant for that. I think it just
needs to be documented. So consider this report a request for
documentation in any case.

> So, if others are reading this, what do you think of making eldoc
> display the diagnostic at point instead of (along with?) whatever it was
> already displaying in the echo area?

Many major modes already use eldoc to show information about the
symbol at point and the echo area is rather disputed by eldoc,
company, etc. I would avoid automatically messaging the error at point
to prevent excessive message switching. But it could be a
customization toggle.