[Feature Request] Add `Resolve` guard

[Sunbreak]

According to https://angular.io/guide/router-tutorial-toh#resolve-pre-fetching-component-data, Angular(Typescript) do have Resolve

According to https://angulardart.dev/guide/router/5, AngularDart is intend to make something similar but have not done: Maybe you should fetch some data before you display the target component.

---

Thank you for taking the time to file an issue!

In order to route, prioritize, and act on this as soon as possible please include:

• [x] Dart SDK Version (dart --version)

Dart SDK version: 2.9.0 (stable) (Fri Jul 31 10:59:48 2020 +0200) on "windows_x64"

• [x] AngularDart Version (i.e. 4.0.0, 5.0.0-alpha+5, MASTER)

angular: ^6.0.0-alpha

• [x] Whether you are using Windows, macOS, or Linux (if applicable)

Windows

• [x] Whether you are using Chrome, Safari, Firefox, Edge (if applicable)

Chrome

• [ ] Any other packages or constraints we should know about

Missing some or all of the above might make the issue take longer or be impossible to act on.

---

For questions consider using Stack Overflow instead: https://stackoverflow.com/questions/tagged/angular-dart

Also consider our Gitter channel for light-weight/quick discussions: https://gitter.im/dart-lang/angular

---