[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.

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• Dart SDK Version (dart --version)

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

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

angular: ^6.0.0-alpha

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