Consolidate some regex OPS

The regular rexpression operation POSIXA works on any of the (currently)
16 posix classes (like \w and [:graph:]) under the regex modifier /a.
This commit creates similar operations for the other modifiers: POSIXL
(for /l), POSIXD (for /d), POSIXU (for /u), plus their complements.

It causes these ops to be generated instead of the ALNUM, DIGIT,
HORIZWS, SPACE, and VERTWS ops, as well as all their variants.  The net
saving is 22 regnode types.

The reason to do this is for maintenance.  As of this commit, there are
now 22 fewer node types for which code has to be maintained.  The code
for each variant was essentially the same logic, but on different
operands.  It would be easy to make a change to one copy and forget to
make the corresponding change in the others.  Indeed, this patch fixes
[perl #114272] in which one copy was out of sync with others.

This patch actually reduces the number of separate code paths to 5:
POSIXA, NPOSIXA, POSIXL, POSIXD, and POSIXU.  The complements of the
last 3 use the same code path as their non-complemented version, except
that a variable is initialized differently.  The code then XORs this
variable with its result to do the complementing or not.  Further, the
POSIXD branch now just checks if the target string being matched is
UTF-8 or not, and then jumps to either the POSIXU or POSIXA code
respectively.  So, there are effectively only 4 cases that are coded:
POSIXA, NPOSIXA, POSIXL, and POSIXU.  (POSIXA doesn't have to worry
about UTF-8, while NPOSIXA does, hence these for efficiency are coded
separately.)

Removing all this code saves memory.  The output of the Linux size
command shows that the perl executable was shrunk by 33K bytes on my
platform compiled under -O0 (.7%) and by 18K bytes (1.3%) under -O2.

The reason this patch was doable was previous work in numbering the
POSIX classes, so that they could be indexed in arrays and bit
positions.  This is a large patch; I didn't see how to break it into
smaller components.

I chose to make this code more efficient as opposed to saving even more
memory.  Thus there is a separate loop that is jumped to after we know
we have to load a swash; this just saves having to test if the swash is
loaded each time through the loop.  I avoid loading the swash until
absolutely necessary.  In places in the previous version of this code,
the swash was loaded when the input was UTF-8, even if it wasn't yet
needed (and might never be if the input didn't contain anything above
Latin1); apparently to avoid the extra test per iteration.

The Perl test suite runs slightly faster on my platform with this patch
under -O0, and the speeds are indistinguishable under -O2.  This is in
spite of these new POSIX regops being unknown to the regex optimizer
(this will be addressed in future commits), and extra machine
instructions being required for each character (the xor, and some
shifting and masking).  I expect this is a result of better caching, and
not loading swashes unless absolutely necessary.

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