bug#59490: 29.0.50; Add C# support

[Yuan Fu]

Eli Zaretskii <eliz@gnu.org> writes:

>> Date: Tue, 22 Nov 2022 22:47:12 +0100
>> From:  Theodor Thornhill via "Bug reports for GNU Emacs,
>>  the Swiss army knife of text editors" <bug-gnu-emacs@gnu.org>
>> 
>> Ok so this works.
>> 
>> Sorry for the mess.
>> 
>> What do you think?
>
> LGTM, thanks.  I'll let Yuan review and install.

Thanks Theo! I’ve merged it. One general comment is that we should have
a "standard" list of features consistent across major modes. I think by
now we’ve worked on font-lock enough to know what those features should
be. I’ll start a discussion on the ML.

Yuan