EntityNeedsSaveInterface should include a method definition for setNeedsSave().

This looks good. It is a possible backwards compatibility break though. Any custom or contrib module that uses EntityNeedsSaveInterface will throw fatal errors if they do not yet implement this method. In practice this might not be a big problem though since we offer EntityNeedsSaveTrait which already includes the method. I did a search on Drupal Code Search for contrib modules that use this interface and as far as I could see this trait is used universally.

Yeah, I guess this is probably OK.

Automatically closed - issue fixed for 2 weeks with no activity.