Enforce conventions around entity file order

[stephenh]

Ideally we like to see entities follow a consistent pattern of:

• The entity class declaration
  • any custom relations, i.e. readonly numberOfBooks = hasPersistedAsyncPropety
  • the constructor
  • methods/async methods with business logic
  • getters/setters
• Validation rules
  • Simple validation rules i.e. config.addRule(a => ...)
  • Reactive validation rules i.e. config.addRule("firstName", a => ...)
• Hooks in the order that Joist runs them
  • beforeCreate
  • beforeUpdate
  • beforeFlush
  • etc.

Approaches

The most traditional approach for this would be an eslint rule(s).

An alternative would be the config API at boot-time what "phase" it's in it, and throw an error if a previous phase is called. However we'd needed exceptions for helper methods (like our internal addCollaborationUtils that adds multiple hooks) and also wouldn't get order of fields/cstr/getters within the class.