feat(core): Add type information to injector.get() (#13785)

- Introduce `InjectionToken<T>` which is a parameterized and type-safe
  version of `OpaqueToken`.

DEPRECATION:
- `OpaqueToken` is now deprecated, use `InjectionToken<T>` instead.
- `Injector.get(token: any, notFoundValue?: any): any` is now deprecated
  use the same method which is now overloaded as
  `Injector.get<T>(token: Type<T>|InjectionToken<T>, notFoundValue?: T): T;`.

Migration
- Replace `OpaqueToken` with `InjectionToken<?>` and parameterize it.
- Migrate your code to only use `Type<?>` or `InjectionToken<?>` as
  injection tokens. Using other tokens will not be supported in the
  future.

BREAKING CHANGE:
- Because `injector.get()` is now parameterize it is possible that code
  which used to work no longer type checks. Example would be if one
  injects `Foo` but configures it as `{provide: Foo, useClass: MockFoo}`.
  The injection instance will be that of `MockFoo` but the type will be
  `Foo` instead of `any` as in the past. This means that it was possible
  to call a method on `MockFoo` in the past which now will fail type
  check. See this example:

```
class Foo {}
class MockFoo extends Foo {
  setupMock();
}

var PROVIDERS = [
  {provide: Foo, useClass: MockFoo}
];

...

function myTest(injector: Injector) {
  var foo = injector.get(Foo);
  // This line used to work since `foo` used to be `any` before this
  // change, it will now be `Foo`, and `Foo` does not have `setUpMock()`.
  // The fix is to downcast: `injector.get(Foo) as MockFoo`.
  foo.setUpMock();
}
```

PR Close #13785

modules/@angular/router/src/router_config_loader.ts

@@ -6,7 +6,7 @@
  * found in the LICENSE file at https://angular.io/license
  */
 
-import {Compiler, ComponentFactoryResolver, Injector, NgModuleFactory, NgModuleFactoryLoader, OpaqueToken} from '@angular/core';
+import {Compiler, ComponentFactoryResolver, InjectionToken, Injector, NgModuleFactory, NgModuleFactoryLoader} from '@angular/core';
 import {Observable} from 'rxjs/Observable';
 import {fromPromise} from 'rxjs/observable/fromPromise';
 import {of } from 'rxjs/observable/of';
@@ -16,10 +16,11 @@ import {mergeMap} from 'rxjs/operator/mergeMap';
 import {LoadChildren, Route} from './config';
 import {flatten, wrapIntoObservable} from './utils/collection';
 
+
 /**
  * @experimental
  */
-export const ROUTES = new OpaqueToken('ROUTES');
+export const ROUTES = new InjectionToken<Route[][]>('ROUTES');
 
 export class LoadedRouterConfig {
   constructor(

modules/@angular/router/src/router_module.ts

@@ -7,7 +7,7 @@
  */
 
 import {APP_BASE_HREF, HashLocationStrategy, Location, LocationStrategy, PathLocationStrategy, PlatformLocation} from '@angular/common';
-import {ANALYZE_FOR_ENTRY_COMPONENTS, APP_BOOTSTRAP_LISTENER, ApplicationRef, Compiler, ComponentRef, Inject, Injector, ModuleWithProviders, NgModule, NgModuleFactoryLoader, NgProbeToken, OpaqueToken, Optional, Provider, SkipSelf, SystemJsNgModuleLoader} from '@angular/core';
+import {ANALYZE_FOR_ENTRY_COMPONENTS, APP_BOOTSTRAP_LISTENER, ApplicationRef, Compiler, ComponentRef, Inject, InjectionToken, Injector, ModuleWithProviders, NgModule, NgModuleFactoryLoader, NgProbeToken, Optional, Provider, SkipSelf, SystemJsNgModuleLoader} from '@angular/core';
 
 import {Route, Routes} from './config';
 import {RouterLink, RouterLinkWithHref} from './directives/router_link';
@@ -36,12 +36,12 @@ const ROUTER_DIRECTIVES = [RouterOutlet, RouterLink, RouterLinkWithHref, RouterL
  * @whatItDoes Is used in DI to configure the router.
  * @stable
  */
-export const ROUTER_CONFIGURATION = new OpaqueToken('ROUTER_CONFIGURATION');
+export const ROUTER_CONFIGURATION = new InjectionToken<ExtraOptions>('ROUTER_CONFIGURATION');
 
 /**
  * @docsNotRequired
  */
-export const ROUTER_FORROOT_GUARD = new OpaqueToken('ROUTER_FORROOT_GUARD');
+export const ROUTER_FORROOT_GUARD = new InjectionToken<void>('ROUTER_FORROOT_GUARD');
 
 export const ROUTER_PROVIDERS: Provider[] = [
   Location,
@@ -301,7 +301,8 @@ export function initialRouterNavigation(
  *
  * @experimental
  */
-export const ROUTER_INITIALIZER = new OpaqueToken('Router Initializer');
+export const ROUTER_INITIALIZER =
+    new InjectionToken<(compRef: ComponentRef<any>) => void>('Router Initializer');
 
 export function provideRouterInitializer() {
   return [