Allow literal / raw values in translation macro / decorator

[buschtoens]

As suggested in #624 (comment).

The translation macro (and soon decorator #623) currently only allow the user to pass keys that will then be used to retrieve the values to be used for interpolating the translation strings: Docs

import Component from '@ember/component':
import { translationMacro as t } from 'ember-intl';

export default Component.extend({
  followersCount: 1,

  // A translation with interpolations. This computed property
  // depends on `count` and will send `{ count: this.followersCount }`
  // in to the translation.
  followersTitle: t('user.followers.title', { count: 'followersCount' })
});

Assume the count variable is static. We can't pass { count: 1 }, instead we need to go through one unnecessary step of redirection by setting followersCount: 1 and then passing { count: 'followersCount' }.

We propose adding a raw function like in ember-awesome-macros / ember-macro-helpers:

import Component from '@ember/component':
import { translationMacro as t, raw } from 'ember-intl';

export default Component.extend({
  // A translation with static interpolations. This computed property
  // has no dependencies (other than the implicit `intl.locale`)
  // and will send `{ count: 1 }`
  followersTitle: t('user.followers.title', { count: raw(1) })
});