bug#46240: Sorting order of read-char-by-name

[Juri Linkov]

>> +*** New user option 'read-char-by-name-sort'.
>
> I suggest to name this read-char-by-name-sort-order.

I always strive to shorten variable names as much as possible.
Overly long names cause problems, especially in completions,
and in any list of variables.  There are docstrings that can
explain in more words about the variable purpose.

>> +*** New user option 'read-char-by-name-group'.
>
> I suggest to name this read-char-by-name-group-by-block.

The intention of this shorter name was to allow more
options to be added to the same variable later.