bug#55086: 28.1; Improve doc of set-fontset-font

[Eli Zaretskii]

> From: Howard Melman <hmelman@gmail.com>
> Date: Sat, 23 Apr 2022 17:51:21 -0400
> 
> The eldoc string for set-fontset-font in Emacs 28 is
> 
>     (NAME TARGET FONT-SPEC &optional FRAME ADD)
> 
> I found NAME and TARGET to be unhelpfully generic.  The
> docstring does say that name is the name of a fontset and
> that TARGET is about characters.
> 
> The elisp manual names the params as:
> 
>     Function: set-fontset-font name character font-spec &optional frame add
> 
> character is an improvement but it should be plural.
> 
> I think they should be the same in both places and
> this would be clearer:
> 
>     (FONTSET CHARACTERS FONT-SPEC &optional FRAME ADD)

Thanks, done.