Close alignment gaps in InstanceKlass

There are a couple of alignment gaps in InstanceKlass that should be filled with rearranging a couple of fields.

  // The NestMembers attribute. An array of shorts, where each is a
  // class info index for the class that is a nest member. This data
  // has not been validated.
  Array<jushort>* _nest_members;

  // The NestHost attribute. The class info index for the class
  // that is the nest-host of this class. This data has not been validated.
  jushort _nest_host_index;

  // Resolved nest-host klass: either true nest-host or self if we are not nested.
  // By always being set it makes nest-member access checks simpler.
  InstanceKlass* _nest_host;

Also misc_flags needs to be a u4, so should be moved down or up.