[FEATURE EMBER_UNIQUE_ID_HELPER] Enable by default
[FEATURE EMBER_UNIQUE_ID_HELPER] Enable by default

Discussed this at today's Ember core team meeting, and we are 👍👍  on enabling this feature by default.
emberjs/ember.js,sly7-7/ember.js,emberjs/ember.js,tildeio/ember.js,tildeio/ember.js,sly7-7/ember.js,emberjs/ember.js,sly7-7/ember.js,tildeio/ember.js