feat(forms): add easy way to switch between forms modules (#9202)

modules/@angular/core/src/platform_directives_and_pipes.ts

@@ -0,0 +1,58 @@
+import {OpaqueToken} from './di';
+
+/**
+   A token that can be provided when bootstrapping an application to make an array of directives
+  * available in every component of the application.
+  *
+  * ### Example
+  *
+  * ```typescript
+  * import {PLATFORM_DIRECTIVES} from '@angular/core';
+  * import {OtherDirective} from './myDirectives';
+  *
+  * @Component({
+  *   selector: 'my-component',
+  *   template: `
+  *     <!-- can use other directive even though the component does not list it in `directives` -->
+  *     <other-directive></other-directive>
+  *   `
+  * })
+  * export class MyComponent {
+  *   ...
+  * }
+  *
+  * bootstrap(MyComponent, [{provide: PLATFORM_DIRECTIVES, useValue: [OtherDirective],
+  multi:true}]);
+  * ```
+  * @stable
+  */
+
+export const PLATFORM_DIRECTIVES: OpaqueToken =
+    /*@ts2dart_const*/ new OpaqueToken('Platform Directives');
+
+/**
+  * A token that can be provided when bootstraping an application to make an array of pipes
+  * available in every component of the application.
+  *
+  * ### Example
+  *
+  * ```typescript
+  * import {PLATFORM_PIPES} from '@angular/core';
+  * import {OtherPipe} from './myPipe';
+  *
+  * @Component({
+  *   selector: 'my-component',
+  *   template: `
+  *     {{123 | other-pipe}}
+  *   `
+  * })
+  * export class MyComponent {
+  *   ...
+  * }
+  *
+  * bootstrap(MyComponent, [{provide: PLATFORM_PIPES, useValue: [OtherPipe], multi:true}]);
+  * ```
+  * @stable
+  */
+
+export const PLATFORM_PIPES: OpaqueToken = /*@ts2dart_const*/ new OpaqueToken('Platform Pipes');