Revamp -Dr handling of /[...]/

Revamp -Dr handling of /[...]/

This revamps the handling of -Dr for bracketed character classes.  There
were bugs introduced earlier in 5.23, and this consolidates the handling
of /d classes so that the interactions can be better considered.  It
tries inverting the portion that is in the bitmap range to see if the
output is shorter, and clearer that way.  And it always makes the
above-bitmap code points show as not-inverted, as that is clearer.

I ran out of time before the freeze, so I had to not invert in some
cases.