feat(forms): add modules for forms and deprecatedForms (#9859)

Closes #9732

BREAKING CHANGE:

We have removed the deprecated form directives from the built-in platform directive list, so apps are not required to package forms with their app. This also makes forms friendly to offline compilation.

Instead, we have exposed three modules:

OLD API:
- `DeprecatedFormsModule`

NEW API:
- `FormsModule`
- `ReactiveFormsModule`

If you provide one of these modules, the default forms directives and providers from that module will be available to you app-wide.  Note: You can provide both the `FormsModule` and the `ReactiveFormsModule` together if you like, but they are fully-functional separately.

**Before:**
```ts
import {disableDeprecatedForms, provideForms} from @angular/forms;

bootstrap(App, [
   disableDeprecatedForms(),
   provideForms()
]);
```

**After:**

```ts
import {DeprecatedFormsModule} from @angular/common;

bootstrap(App, {modules: [DeprecatedFormsModule] });
```

-OR-

```ts
import {FormsModule} from @angular/forms;

bootstrap(App, {modules: [FormsModule] });
```

-OR-

```ts
import {ReactiveFormsModule} from @angular/forms;

bootstrap(App, {modules: [ReactiveFormsModule] });
```

You can also choose not to provide any forms module and run your app without forms.

Or you can choose not to provide any forms module *and* provide form directives at will.  This will allow you to use the deprecatedForms API for some components and not others.

```
import {FORM_DIRECTIVES, FORM_PROVIDERS} from @angular/forms;

@Component({
   selector: some-comp,
   directives: [FORM_DIRECTIVES],
   providers: [FORM_PROVIDERS]
})
class SomeComp
```

modules/@angular/forms/src/form_providers.ts

@@ -6,64 +6,37 @@
  * found in the LICENSE file at https://angular.io/license
  */
 
-
-import {COMMON_DIRECTIVES, FORM_DIRECTIVES as OLD_FORM_DIRECTIVES, FORM_PROVIDERS as OLD_FORM_PROVIDERS} from '@angular/common';
-import {CompilerConfig} from '@angular/compiler';
-import {PLATFORM_DIRECTIVES, PLATFORM_PIPES, Type} from '@angular/core';
-
-import {FORM_DIRECTIVES as NEW_FORM_DIRECTIVES} from './directives';
-import {RadioControlRegistry as NewRadioControlRegistry} from './directives/radio_control_value_accessor';
-import {ListWrapper} from './facade/collection';
-import {FormBuilder as NewFormBuilder} from './form_builder';
-
+import {AppModule, Type} from '@angular/core';
+import {FORM_DIRECTIVES, REACTIVE_FORM_DIRECTIVES} from './directives';
+import {RadioControlRegistry} from './directives/radio_control_value_accessor';
+import {FormBuilder} from './form_builder';
 
 
 /**
  * Shorthand set of providers used for building Angular forms.
- *
- * ### Example
- *
- * ```typescript
- * bootstrap(MyApp, [FORM_PROVIDERS]);
- * ```
- *
  * @experimental
  */
-export const FORM_PROVIDERS: Type[] = /*@ts2dart_const*/[NewFormBuilder, NewRadioControlRegistry];
-
-function flatten(platformDirectives: any[]): any[] {
-  let flattenedDirectives: any[] = [];
-  platformDirectives.forEach((directives) => {
-    if (Array.isArray(directives)) {
-      flattenedDirectives = flattenedDirectives.concat(directives);
-    } else {
-      flattenedDirectives.push(directives);
-    }
-  });
-  return flattenedDirectives;
-}
-
+export const FORM_PROVIDERS: Type[] = /*@ts2dart_const*/[RadioControlRegistry];
 
 /**
+ * Shorthand set of providers used for building reactive Angular forms.
  * @experimental
  */
-export function disableDeprecatedForms(): any[] {
-  return [{
-    provide: CompilerConfig,
-    useFactory: (platformDirectives: any[], platformPipes: any[]) => {
-      const flattenedDirectives = flatten(platformDirectives);
-      ListWrapper.remove(flattenedDirectives, OLD_FORM_DIRECTIVES);
-      return new CompilerConfig({platformDirectives: flattenedDirectives, platformPipes});
-    },
-    deps: [PLATFORM_DIRECTIVES, PLATFORM_PIPES]
-  }];
+export const REACTIVE_FORM_PROVIDERS: Type[] =
+    /*@ts2dart_const*/[FormBuilder, RadioControlRegistry];
+
+/**
+ * The app module for forms.
+ * @experimental
+ */
+@AppModule({providers: [FORM_PROVIDERS], directives: FORM_DIRECTIVES, pipes: []})
+export class FormsModule {
 }
 
 /**
+ * The app module for reactive forms.
  * @experimental
  */
-export function provideForms(): any[] {
-  return [
-    {provide: PLATFORM_DIRECTIVES, useValue: NEW_FORM_DIRECTIVES, multi: true}, FORM_PROVIDERS
-  ];
-}
+@AppModule({providers: [REACTIVE_FORM_PROVIDERS], directives: REACTIVE_FORM_DIRECTIVES, pipes: []})
+export class ReactiveFormsModule {
+}