Sets should construct with array values.
Speed up Map/Set by using a hidden property for backing storage.

Map/Set used a WeakMap to associate a hidden [[MapData]] with a given
Map or Set.  This caused a huge slowdown.  If we don't need to use WeakMaps
and don't care about users seeing extra hidden properties on Map/Set
instances, then we can get a big speedup.
Remove minimized source, since it's out of date.