Prop type validation

[aalin]

It would be nice if it was possible to specify prop types.

Something like T::Struct in Sorbet maybe.

:ruby
  prop :description, String, nil?: true
  prop :count, Integer
  prop :onclick, HandlerRef
%div
  = if $description
    %p= $description
  %p Count: #{$count}
  %div
    %button{onclick: $onclick}