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/compiler-cli/integrationtest/src/entry_components.ts

@@ -6,7 +6,7 @@
  * found in the LICENSE file at https://angular.io/license
  */
 
-import {ANALYZE_FOR_ENTRY_COMPONENTS, Component, ComponentFactoryResolver, Inject, OpaqueToken} from '@angular/core';
+import {ANALYZE_FOR_ENTRY_COMPONENTS, Component, ComponentFactoryResolver, Inject, InjectionToken} from '@angular/core';
 
 import {BasicComp} from './basic';
 
@@ -15,7 +15,7 @@ export class CompWithEntryComponents {
   constructor(public cfr: ComponentFactoryResolver) {}
 }
 
-export const SOME_TOKEN = new OpaqueToken('someToken');
+export const SOME_TOKEN = new InjectionToken('someToken');
 
 export function provideValueWithEntryComponents(value: any) {
   return [

modules/@angular/compiler-cli/integrationtest/src/features.ts

@@ -7,21 +7,21 @@
  */
 
 import * as common from '@angular/common';
-import {CUSTOM_ELEMENTS_SCHEMA, Component, Directive, EventEmitter, Inject, NgModule, OpaqueToken, Output} from '@angular/core';
+import {CUSTOM_ELEMENTS_SCHEMA, Component, Directive, EventEmitter, Inject, InjectionToken, NgModule, Output} from '@angular/core';
 import {Observable} from 'rxjs/Observable';
 
 import {wrapInArray} from './funcs';
 
-export const SOME_OPAQUE_TOKEN = new OpaqueToken('opaqueToken');
+export const SOME_INJECTON_TOKEN = new InjectionToken('injectionToken');
 
 @Component({
   selector: 'comp-providers',
   template: '',
   providers: [
     {provide: 'strToken', useValue: 'strValue'},
-    {provide: SOME_OPAQUE_TOKEN, useValue: 10},
+    {provide: SOME_INJECTON_TOKEN, useValue: 10},
     {provide: 'reference', useValue: common.NgIf},
-    {provide: 'complexToken', useValue: {a: 1, b: ['test', SOME_OPAQUE_TOKEN]}},
+    {provide: 'complexToken', useValue: {a: 1, b: ['test', SOME_INJECTON_TOKEN]}},
   ]
 })
 export class CompWithProviders {

modules/@angular/compiler-cli/integrationtest/src/module_fixtures.ts

@@ -7,7 +7,7 @@
  */
 
 import {LowerCasePipe, NgIf} from '@angular/common';
-import {ANALYZE_FOR_ENTRY_COMPONENTS, Component, ComponentFactoryResolver, Directive, Inject, Injectable, Input, ModuleWithProviders, NgModule, OpaqueToken, Pipe} from '@angular/core';
+import {ANALYZE_FOR_ENTRY_COMPONENTS, Component, ComponentFactoryResolver, Directive, Inject, Injectable, InjectionToken, Input, ModuleWithProviders, NgModule, Pipe} from '@angular/core';
 
 @Injectable()
 export class SomeService {
@@ -48,7 +48,7 @@ export class CompUsingRootModuleDirectiveAndPipe {
 export class CompUsingLibModuleDirectiveAndPipe {
 }
 
-export const SOME_TOKEN = new OpaqueToken('someToken');
+export const SOME_TOKEN = new InjectionToken('someToken');
 
 export function provideValueWithEntryComponents(value: any) {
   return [