bug#50178: 28.0.50; Size of echo area does not account for line-spacing

[Eli Zaretskii]

> From: Óscar Fuentes <ofv@wanadoo.es>
> Cc: Eli Zaretskii <eliz@gnu.org>,  50178-done@debbugs.gnu.org
> Date: Wed, 25 Aug 2021 12:49:39 +0200
> 
> As useful as it would be an API that returns how many lines fit on a
> given window.

What is a "line" for this purpose?  The notion of a "canonical line"
is well defined, and that is what we use.  Any other notion will have
to be defined first, and it isn't easy, I can tell you.

> Or, on this case, max-mini-window-height being a true
> indication of the capacity of the mini window on terms of the current
> display settings, which is what the users want 99.9% of the time.

Unless you counted only yourself in those 99.9%, it is a strange thing
to say about the modern Emacs.  It's as if you wanted to go back to
Emacs 18, where all lines were the same height.