1.0.43.45: More type-directed constant folding

1.0.43.45: More type-directed constant folding

 * 1.0.30.2 introduced logic to use MEMBER-TYPEs during constant
   propagation.  This commit uses SINGLETON-TYPE-P to extend that
   logic to more types (NUMERIC and CHARACTER-SET).

 * This exposes additional constant-folding opportunities in
   src/code/bit-bash.lisp; the necessary definitions are now available
   at compile-time.