Implement @LazyInject decorator

[guyca]

This differs from the @LateInject decorator in that the dependency will be resolved the first time it's accessed without needing to call Obsidian.inject(this) explicitly.

API

@Injectable(ApplicationGraph)
class Injected {
  @LazyInject() foo!: Foo;

  constructor() {
    // foo is unresolved
    this.foo.bar(); // foo is resolved on demand
  }
}

Implementation

In order to achieve this behavior, the @LazyInject decorator should probably return a Proxy which will resolve the dependency when it's required.