New candidate JEP: 500: Prepare to Make Final Mean Final

[Mark Reinhold]

https://openjdk.org/jeps/500

  Summary: Issue warnings about uses of deep reflection to mutate
  final fields.  These warnings aim to prepare developers for a future
  release that ensures integrity by default by restricting final field
  mutation, which will make Java programs safer and potentially faster.
  Application developers can avoid both current warnings and future
  restrictions by selectively enabling the ability to mutate final fields
  where essential.

- Mark