Wildcard initialization order produced confusing code

Because WildcardType.bound may not be initialized before a wildcard
is used in a subtype question, the following code is used to determine
the upper bound of super bounded wildcards:

  WildcardType w = (WildcardType)t;
  w.bound == null ? syms.objectType : w.bound.bound;

This is unfortunate and should be addressed by rethinking how wildcards
are set up.