bug#42064: 28.0.50; German "Sharp S" is capitalized inconsistenly

[Eli Zaretskii]

> From: "Philip K." <philip@warpmail.net>
> Date: Fri, 26 Jun 2020 20:44:55 +0200
> 
> The german "Sharp S" (ß), seems to be capitalized inconsistenly,
> depending on the system:
> 
> - The german postfix input method, typing "SZ" inserts "ẞ"
> - If a buffer already contains a "ß", running upcase-dwim generates
>   "SS". Lowercasing this results in "ss" unsurprisingly, while "ẞ"
>   generates "ß".
> 
> Both behaviours are fine in their own right, but don't seem to make a
> lot of sense together.

Do you have a proposal for how to improve this?  The problem, AFAIU,
is that there are different preference, each one of which is
legitimate, so the only way forward, it seems, is to introduce some
user options to select the desired behavior.