[FEAT] Updates decorator implementation to stage 1

[pzuraq]

This moves us back to stage 1 decorators for our internal decorator implementation. It also reverts to using a Symbol instead of a WeakMap for @tracked values. This is overall a better for perf, assuming we can assign the value of the symbol in the constructor via an initializer. Unfortunately stage 1 decorators don't allow this, but fortunately it should be very easy to add a babel transform specifically for @tracked that does, so we can get the ideal performance.

[GavinJoyce]

I'm seeing Error: Assertion Failed: The options object passed to tracked() may only contain a 'value' or 'initializer' property, not both. Received: [kind,key,placement,descriptor,initializer] for simple @tracked count = 1; in a recent app created with the ember-octane-app-blueprint. Perhaps caused by this change?

Here's the component js:

import Component from '@glimmer/component';
import { tracked } from '@glimmer/tracking';

export default class CounterComponent extends Component {
  @tracked count = 1;

  increment() {
    this.count++;
  }
}

The error occurs with the latest ember-source sha (2ed6adf8f3b9386e02808af7caaa0feec290a144), not with a sha from yesterday (d92c83887d58fa0aaf9ffcf51d894044f3711e81)

[pzuraq]

The octane app blueprint needs to be updated to use the stage 1 decorator transforms. We can install @ember-decorators/babel-transforms@v2 for now

[GavinJoyce]

Thanks, here's a PR to downgrade babel-transforms in the octane blueprints:

ember-cli/ember-octane-blueprint#58