Speed up skip-chars-{forward|reverse} with char classes

Speed up skip-chars-{forward|reverse} with char classes

* src/regex-emacs.h (re_wctype_t): Add RECC_NUM_CLASSES.
* src/syntax.c (skip_chars, in_classes): Use an array on the stack
instead of a Lisp list for storing character classes.
Don't check all classes if there is a match in one.
Remove useless handle_iso_classes argument.