[vector] binary operations with a scalar

[Vladimir Ivanov]

> 
> I like this but suggest we keep the code marginally simpler and revisit if we have performance concerns. If we don’t make intrinsic the broadcast+op combination i think something like this is probably ok for now:
> 
>     @Override
>     @ForceInline
>     public Int256Vector add(int o) {
>         return add(Int256Species.broadcastImpl(o));
>     }

If we don't care about optimized default implementation, then even 
simpler variant should work:

      @Override
      @ForceInline
      public Int256Vector add(int i) {
          return add(species().broadcast(i));
      }

add(), species(), and broadcast() methdos are trivially inlined since 
the new method is declared in concrete vector class.

Best regards,
Vladimir Ivanov