feat: add fromPropertyChange source

[alexlafroscia]

Idea: turn a stream of property changes into an Observable.

import { fromPropertyChange } from 'ember-observable';

export default class Foo extends EmberObject {
  key = value;

  init() {
    super.init(...arguments):

    const observable = fromPropertyChange(this, 'key');
    observable.subscribe(value => {
      console.log(value);
    });
  }
}

• Automatically unsubscribe once the object is destroyed -- no more need for removeObserver directly
• Could subscribe use this internally?

[alexlafroscia]

Automatically unsubscribe once the object is destroyed -- no more need for removeObserver directly

Probably not necessary, and this would require injecting code into willDestroy -- not great

Could unsubscribe use this internally?

Turns out the safe answer is "no" -- I saw something earlier today saying that an observer should not create a subscription, and refactoring to use fromPropertyChange in the subscribe decorator would require that.