regcomp.c: Rename a macro, fix-up comments

This very recently introduced macro's name could be clearer, and it can
be used in another place, and the comment concerning that is slightly
inaccurate.
mktables: Add table for chars with multi-char fold

This will be used in a later commit
regen/mk_invlists.pl: Make list for multi-fold chars

This causes charclass_invlists.h to have a new list of all the
characters whose fold is a sequence of more than one character.
PATCH: [perl #89774] multi-char fold + its fold in char class

The design for handling characters that fold to multiple characters when
the former are encountered in a bracketed character class is defective.
The ticket reads, "If a bracketed character class includes a character
that has a multi-char fold, and it also includes the first character of
that fold, the multi-char fold will never be matched; just the first
character of the fold.".   Thus, in the class /[\0-\xff]/i, \xDF will
never be matched, because its fold is 'ss', the first character of
which, 's', is also in the class.

The reason the design is defective is that it doesn't allow for
backtracking and trying the other options.

This commit solves this by effectively rewriting the above to be
/ (?: \xdf | [\0-\xde\xe0-\xff] ) /xi.  And so the backtracking gets
handled automatcially by the regex engine.
regcomp.c: Fix-up indentaion; no code changes

Indent a newly-formed block
regex: Remove old code that tried to handle multi-char folds

A recent commit has changed the algorithm used to handle multi-character
folding in bracketed character classes.  The old code is no longer
needed.
regex: Splice out no longer used array element

A recent commit removed all uses of an array element in the middle of an
array.  This moves up the elements that followed it.
regex: Rename macro to reflect its narrowed use

This macro is now only used under locale; its other use has now been
removed.  Change the name to reflect its only use.
regex: White-space, comment only; no code changes

This outdents code that just had its containing block removed, and
reflows its comments to fill 79 columns; and does some other white space
adjustments, plus a typo in a comment.
utf8.h: Correct some values for EBCDIC

It occurred to me that EBCDIC has different maximums for the number of
bytes a character can occupy.  This moves the definition in utf8.h to
within an #ifndef EBCDIC, and adds the correct values to utfebcdic.h
regexp.t: Add 'no warnings "utf8";

This .t works fine unless there are failures that it tries to output,
and the handle hasn't been opened using utf8.  Because we aren't sure if
that operation works, just turn off warnings.
regcomp.c: Don't set /i in start class unless /l

There is a deficiency in the optimizer in which it doesn't get rid of
flags that it should.  One of these is if it should match /i or not.
Currently it always (perhaps not quite, I don't know) assumes that it
should match under /i, yielding false positives and slowing things down.
But a recent commit changed the flag that tells it to do this, so that it
only gets set if /l is also specified.  There is already existing code to
work around the optimizer deficiency for /l.  This commit just moves the
/i flag handling to that existing code, so it won't get invoked unless
/l is specified.