Add ViewData for internal view owned state

[Zoxc]

This add ViewData for internal view owned state.

Storing view state in ViewData instead of ViewState has a couple of benefits:

• It can be accessed in passes without a hash map lookup.
• Decorators can write to it directly instead of using update messages for the initial value.
  The downside is that updating ViewData by a message requires walking the view tree, which is probably more expensive.

Overall I think it's a good tradeoff as it favors view passes and view creation which does seem to be the slowest parts.

The style field is moved from ViewState to ViewData.