feat: add new rule private-states

[jpradelle]

Add a new rule to enforce component reactive states to be private or protected

As defined in lit documentation https://lit.dev/docs/components/properties/#internal-reactive-state

Internal reactive state refers to reactive properties that are not part of the component's public API.
 These state properties don't have corresponding attributes, and aren't intended to be used from
 outside the component. Internal reactive state should be set by the component itself.