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/common/src/common_directives.ts

@@ -9,8 +9,6 @@
 import {Type} from '@angular/core';
 
 import {CORE_DIRECTIVES} from './directives';
-import {FORM_DIRECTIVES} from './forms-deprecated';
-
 
 /**
  * A collection of Angular core directives that are likely to be used in each and every Angular
@@ -57,4 +55,4 @@ import {FORM_DIRECTIVES} from './forms-deprecated';
  *
  * @experimental Contains forms which are experimental.
  */
-export const COMMON_DIRECTIVES: Type[][] = /*@ts2dart_const*/[CORE_DIRECTIVES, FORM_DIRECTIVES];
+export const COMMON_DIRECTIVES: Type[][] = /*@ts2dart_const*/[CORE_DIRECTIVES];

modules/@angular/common/src/forms-deprecated.ts

@@ -18,8 +18,9 @@
  * Forms providers are not included in default providers; you must import these providers
  * explicitly.
  */
-import {Type} from '@angular/core';
+import {AppModule, Type} from '@angular/core';
 
+import {FORM_DIRECTIVES} from './forms-deprecated/directives';
 import {RadioControlRegistry} from './forms-deprecated/directives/radio_control_value_accessor';
 import {FormBuilder} from './forms-deprecated/form_builder';
 
@@ -57,3 +58,18 @@ export {NG_ASYNC_VALIDATORS, NG_VALIDATORS, Validators} from './forms-deprecated
  * @experimental
  */
 export const FORM_PROVIDERS: Type[] = /*@ts2dart_const*/[FormBuilder, RadioControlRegistry];
+
+
+/**
+ * The app module for the deprecated forms API.
+ * @deprecated
+ */
+@AppModule({
+  providers: [
+    FORM_PROVIDERS,
+  ],
+  directives: FORM_DIRECTIVES,
+  pipes: []
+})
+export class DeprecatedFormsModule {
+}