code: public ZoneRulesBuilder addWindowForever(ZoneOffset standardOffset) {
          return addWindow(standardOffset, LocalDateTime.MAX, TimeDefinition.WALL);
      }
docs: Adds a window that applies until the end of time to the builder that can be
  used to filter a set of rules.
  <p>
  This method defines and adds a window to the zone where the standard offset is specified.
  The window limits the effect of subsequent additions of transition rules
  or fixed savings. If neither rules or fixed savings are added to the window
  then the window will default to no savings.
  <p>
  This must be added after all other windows.
  No more windows can be added after this one.
  
  @param standardOffset  the standard offset, not null
  @return this, for chaining
  @throws IllegalStateException if a forever window has already been added