bug#41531: 28.0.50; proper Eldoc async support

[Andrii Kolomoiets <andreyk.mad@gmail.com>]

João Távora <joaotavora@gmail.com> writes:

> Hello again gang,

Hi João,

> When applied, these improvements result in a substantial reduction of
> Eglot's documentation handling code.  Yes, Andrii, that means all our
> hand-crafted, hard work of doc handling functions is soon gone,
> including the awkward eglot-put-doc-in-help-buffer,
> eglot-auto-display-help-buffer and the *eglot-help* buffer.
>
> Feels sad but also good, because deleted code is good code.  And it's
> not in vain because your feedback and testing was fundamental here.  And
> the good news is that the logic problems about blinking and giving
> priority to some docs is gone.

I for one completely support moving documentation handling code to
eldoc.

I was planning to remove the eglot-put-doc-in-help-buffer variable in
the near future PR as well as the use of the eglot--message function for
the documentation display ;-)

However, after briefly using new Eldoc and Eglot I found some issues
that, I hope, we can fix:

1. Display only first line of the hover info.  Again :-)

2. The hover info is sometimes displayed right before the signature info
making the echo area to "blink".  I suppose this must be fixed on Eglot
side by not requesting both the hover and the signature infos at the
same time.

3. That IMO useless "...truncated, see *help* buffer" message is moved
to Eldoc.  Do we really need to show this message every time?  That one
last line can be used to show additional documentation.

Hadn't a chance to take a closer look at the code, so reporting those
issues is the most I can do for now.

Thanks!