[@glimmer/component] Make component generic over args

[mike-north]

This allows TS consumers to (optionally) benefit from formalizing the interface a component has with the outside world.

import Component from '@glimmer/component';

export default class Foo extends Component<{ word: string}> {

  printWord() {
     console.log(this.args.word); // type-safe access to args
  }
}

[NullVoxPopuli]

🙌 🎉

[rwjblue]

Change looks good to me, and mirrors what was done in the types for the "ember consumers"

glimmer.js/packages/@glimmer/component/addon/index.ts

Line 9 in b9a0165

class GlimmerComponent<T> extends _GlimmerComponent<T> {