DEV: implements part of ember-truth-helpers (PR #12667)

The implemented helpers, are helpers which might be in Ember core in the future:

  • and
  • or
  • not
  • eq
  • not-eq
  • lt
  • lte
  • gt
  • gte

They follow the implementation of ember-truth-helpers: GitHub - jmurphyau/ember-truth-helpers: Ember HTMLBars Helpers for {{if}} & {{unless}}: not, and, or, eq & is-array

Note 1: Ember rfcs are still debating going with {{not-eq}} or {{neq}}, should be easy to support in the future whatever is finally chosen.

Note 2: this commit also moves to its own addon, and removes the {{not}} test, to simplify further updates.