ENH: disentangle testing and quoting of regex characters

- originally had tests for regex meta characters strewn across
  regExp classes as well as wordRe, keyType, string.
  And had special-purpose quotemeta static function within string
  that relied on special naming convention for testing the meta
  characters.

  The regex meta character testing/handling now relegated entirely
  to the regExp class(es).
  Relocate quotemeta to stringOps, with a predicate.

- avoid code duplication. Reuse some regExpCxx methods in regExpPosix