Which @angular/* package(s) are relevant/releated to the feature request?

router

Description

The Angular router's current architecture is problematic for a couple big reasons:

• It is not extensible. Developers cannot easily extend or change the Router's functionality to support features that would be useful to their applications. Instead, these features have to be built in to the core Router code and exposed through some endpoint (i.e. RouteReuseStrategy, some option on ExtraOptions which is used as an switch in the internal code, etc.)
• It is not tree shakeable. Due to its non-modular nature, almost all features (lazy loading, guards, resolvers) are generally baked in to the Router's internals unless explicitly configurable through a Strategy that can provide a no-op implementation. Simple applications that do not use these features still incur the bundle size cost.

Proposed solution

Because of the above two problems, we're often quite limited on what features we can implement. The router should be rearchitected with the following goals in mind:

• Tree-shakeability
• More configurable features, such as
  • Change Route guard and resolver ordering to follow route parent/child hierarchy #24187
  • Async guards should have the option to wait for previous guards to finish #40577
  • Perhaps Router Resolve shouldn't wait for Observable to Complete? #10556 / Add wait/no-wait asynchronous policy control to router resolves #24956
  • feat(router): Cascading route support #16416
  • Configurable browser history management, for example
    • Ability to use the upcoming App History API
    • Add option to not reset Url and Router state to Angular Router on Navigation Errors #42915
    • Ability to fix issues like Deactivation Guard breaks the routing history #13586 without having to wait for the baked-in fix
• General ability to use @angular/router to build custom routing solutions, which will likely require exposing more of the router internals such as:
  • Add UrlTree utilities/helpers to public API #38951
  • Provide an official way to access the module/injector for a route #25630 / Expose '_loadedConfig' in a public way. #24069

Alternatives considered

N/A