bug#39254: 26.3 and 27.0.50; The manual is inconsistent about the <Alt> modifier and C-x 8

[Eli Zaretskii]

> From: jorge+list@disroot.org (Jorge P. de Morais Neto)
> Date: Thu, 23 Jan 2020 10:42:59 -0300
> 
> Hi.  The manual section [[info:emacs#Modifier Keys]] says "the standard
> key bindings in Emacs do not include any characters with these modifiers"
> (referring to <Super>, <Hyper> and <Alt>).  However,
> [[info:emacs#Inserting Text]] says "a working Alt key acts like `C-x
> 8'".  Also, the wording in the latter manual section makes it seem that
> any key sequence starting with the `C-x 8' prefix works with <Alt>, but,
> according to my testing (with C-x @ a), that does not hold for `C-x 8
> RET'.

Thanks, I fixed these inaccuracies.