feat(intl): add @intl decorator

[buschtoens]

Closes ember-intl/ember-intl#392 (comment).

From the README.md:

A generic decorator that implicitly injects the intl service and creates a
computed property that depends on the current locale and any further optional
dependent keys passed to the decorator.

The decorated method or (arrow) function is bound to the class instance the
decorator is used on and invoked with two parameters:

• intl: the intl service, that you can use to call any method on
• propertyKey: the name of the decorated property

The return value is used as the value of the computed property.

import Component from '@ember/component';
import { intl } from '@ember-intl/decorators';

class ExampleComponent extends Component {
  amount = 1.23;
  currency = 'EUR';

  @intl('amount', 'currency')
  formatted = intl =>
    intl.formatNumber(this.amount, {
      style: 'currency',
      currency: this.currency
    });
}

[buschtoens]

Depends on ember-decorators/ember-decorators#318 for legacy decorators compatibility, which we don't explicitly test for yet. One could argue that this is responsibility of @ember-decorators/utils (and they do test for it), but adding some more tests here would not hurt, I guess.

[buschtoens]

Depends on ember-intl/ember-intl#708

[buschtoens]

🎉 This PR is included in version 0.2.0 🎉

The release is available on:

• npm package (@latest dist-tag)
• GitHub release

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