Create spans via decorators

[ewhauser]

Creating a span for every component using component lifecycle events can be tedious. A better (?) approach could be to inject tracing behavior as a mixin via decorators:

@Component({
   selector: 'app-heroes',
   templateUrl: './heroes.component.html'
 })
@Trace({start: OnInit, end: OnDestroy})
 export class HeroesComponent { 
  localspan: LocalSpan;

The current problem with this approach is it breaks tree shaking for your application:

https://blog.nrwl.io/metaprogramming-higher-order-components-and-mixins-with-angular-ivy-75748fcbc310

so this shouldn't be built until Angular Ivy is released.