regex: Use #define for number of bits in ANYOF

ANYOF nodes (for bracketed character classes) currently are for code
points 0-255.  This is the first step in the eventual making that size
configurable.  This also renames a static function, as the domain may
not necessarily be 'latin1'
Move _get_regclass_nonbitmap_data() to regcomp.c

This function, though mostly used by regexec.c and previously contained
therein, relies on the particular data structure in regcomp.c, so it
makes sense to move it adjacent to the code that generates the
structure.  Future commits will add function calls to this function that
are (currently) only in regcomp.c, and so will tie it tighter to that
file.

This just moves the code with surrounding #ifdef, adds a couple of blank
lines, removes some trailing white space, and adjusts the comments.  No
other changes were made.
regcomp.c: Reorder cases: in switch

This makes it slightly more reader-friendly
Avoid redundant text -in -Dr output

There is an optimization in regcomp.c which saves memory when used, but
which caused -Dr output to display the same code points twice.
I didn't add a test to ext/re/t/regop.t because this only happens for a
Unicode property, under certain circumstances, and that triggers a lot
of other regex patterns to be compiled which are subject to change, so
the test would frequently have to be updated.  This only affects
debugging output anyway.
regcomp.c: Swap 'else' clauses.

It's easier to comprehend a tiny else clause followed by a large one and
vice-versa.  This is in preparation for further changes in future
commits.
regcomp.c: Avoid function call overhead

We don't need to call a function to convert from UTF-8 when the value is
invariant in and out of UTF-8.
perlop: Note that negative rep now warns

This doc change was missed in b3211734a7d280a8b7c6acaaba333f8f6a314675
but it appears that this will not be reverted, so safe to go in now
without having to worry very much about synchronizing should there be a
reversion
perlrecharclass: Remove now-irrelevant text

v5.21 now uses the same definition of white-space that this gives, so
there is no need to repeat it here, and is misleading because it says
this is different from the other definition.