reduce number of calls to add_cp_to_invlist()

reduce number of calls to add_cp_to_invlist()

Both S_get_ANYOF_cp_list_for_ssc() and S_put_charclass_bitmap_innards()
have tight loops that iterate over a bitmap and calls add_cp_to_invlist()
for each bit set.

add_cp_to_invlist() is a fairly wrapper around _add_range_to_invlist()
which create a new invlist to hold the range and then calls
_invlist_union() to perform the add.  This is moderately expensive.

Instead of indirectly calling _add_range_to_invlist(), where it's
simple to do so, instead look for ranges of bits set in the bitmaps
and call _add_range_to_invlist() directly.

This changed the cachegrind output from running:

  ./perl -e 'qr/_?[\W_]/;'

from:

==23406== I   refs:      1,752,149
==23406== I1  misses:        5,405
==23406== LLi misses:        3,588
==23406== I1  miss rate:      0.30%
==23406== LLi miss rate:      0.20%
==23406==
==23406== D   refs:        683,242  (414,061 rd   + 269,181 wr)
==23406== D1  misses:       13,370  (  7,646 rd   +   5,724 wr)
==23406== LLd misses:        7,025  (  3,417 rd   +   3,608 wr)
==23406== D1  miss rate:       1.9% (    1.8%     +     2.1%  )
==23406== LLd miss rate:       1.0% (    0.8%     +     1.3%  )
==23406==
==23406== LL refs:          18,775  ( 13,051 rd   +   5,724 wr)
==23406== LL misses:        10,613  (  7,005 rd   +   3,608 wr)
==23406== LL miss rate:        0.4% (    0.3%     +     1.3%  )

to:

==25041== I   refs:      1,189,412
==25041== I1  misses:        5,218
==25041== LLi misses:        3,598
==25041== I1  miss rate:      0.43%
==25041== LLi miss rate:      0.30%
==25041==
==25041== D   refs:        440,339  (283,047 rd   + 157,292 wr)
==25041== D1  misses:       11,872  (  7,257 rd   +   4,615 wr)
==25041== LLd misses:        7,024  (  3,417 rd   +   3,607 wr)
==25041== D1  miss rate:       2.6% (    2.5%     +     2.9%  )
==25041== LLd miss rate:       1.5% (    1.2%     +     2.2%  )
==25041==
==25041== LL refs:          17,090  ( 12,475 rd   +   4,615 wr)
==25041== LL misses:        10,622  (  7,015 rd   +   3,607 wr)
==25041== LL miss rate:        0.6% (    0.4%     +     2.2%  )

ie. from 1.75 million instructions to 1.19 million instructions.