vte3: implement get/set rewrap_on_resize

Implement:
<setter>
Vte::Terminal#rewrap_on_resize= boolean
Vte::Terminal#set_rewrap_onresize(boolean)
<getter>
Vte::Terminal#rewrap_on_resize

```ruby
terminal = Vte::Terminal.new
terminal.rewrap_on_resize = true
p terminal.rewrap_on_resize #=> true
```

repoted by dark-yux. Thanks!!

fixes #257