bug#65902: 29.0.92; emacsclient-mail.desktop fails due to complicated escaping

[Eli Zaretskii]

> From: Andreas Schwab <schwab@linux-m68k.org>
> Cc: stefankangas@gmail.com,  jporterbugs@gmail.com,  sbaugh@catern.com,
>   sbaugh@janestreet.com,  65902@debbugs.gnu.org
> Date: Fri, 22 Sep 2023 15:23:51 +0200
> 
> On Sep 22 2023, Eli Zaretskii wrote:
> 
> > What do you mean by "arbitrary arguments"? what kind of arguments need
> > to be passed here that are not currently supported?
> 
> %u

This contradicts what I see in the *desktop files.  They use shell
commands and features.  See, for example, emacsclient.desktop and
emacsclient-mail.desktop.