Re: `texinfo.tex` doesn't work with xetex

[Gavin Smith]

On Sat, Aug 20, 2022 at 07:17:32AM +0000, Werner LEMBERG wrote:
> 
> [texinfo.tex 2022-08-21.14]
> 
> Processing
> 
> ```
> \input texinfo
> 
> @documentencoding UTF-8
> 
> @include ae/lily-651af4bb.texidoc
> 
> @bye
> ```
> 
> (it's not necessary to actually have an include file) with
> 
> ```
> PDFTEX=xetex texi2pdf
> ```
> 
> aborts with
> 
> ```
> Bad character code (185937).
> <to be read again> 
>                    a
> a->@ifpassthroughchars a@else a
>                                @fi 
> l.5 @include ae/lily-651a
>                          f4bb.texidoc
> ```
> 

I believe I've fixed this.  There were at least two problems, both
caused by a recent change to allow ASCII characters to be output with
@U, by giving the Unicode code point value.  (This is unnecessary,
obviously.)  I've disabled this code and it should work okay now.

The two problems were:
* The definition of some characters used \char but I didn't terminate
the argument.  For example, - would become \char"2d and then in the
example, following characters would be read as part of the number,
become \char"2d651a which XeTeX is reporting as too big a number.

* That was easy to fix, but then files would still not process properly
because all characters were typesetting literally, so "@bye" would
typeset a literal "@" followed by "bye".

While it's consistent to allow @U to be used for ASCII characters,
it doesn't appear to offer any benefit.  If the code is re-enabled
the second point here would still need to be fixed.