Apply caselessness to each element added to a class, rather than all at
finalize time (which required separated ucp dnf and-ucp working data).
Unifies the behaviour of AsciiComponentClass and Utf8ComponentClass in
this respect.
ComponentClass::class_empty should only be used on finalized classes to
determine whether a given class contains any elements; it should not
take the cr_ucp or cps_ucp into account, as they have been folden in by
the finalize call.
Fixes our failure to identify that the pattern /[^\D\d]/8W can never
match.
