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/directives.ts

@@ -44,7 +44,18 @@ export {NgSelectOption, SelectControlValueAccessor} from './directives/select_co
 export {NgSelectMultipleOption, SelectMultipleControlValueAccessor} from './directives/select_multiple_control_value_accessor';
 export {MaxLengthValidator, MinLengthValidator, PatternValidator, RequiredValidator} from './directives/validators';
 
+const SHARED_FORM_DIRECTIVES: Type[] = /*@ts2dart_const*/[
+  NgSelectOption, NgSelectMultipleOption, DefaultValueAccessor, NumberValueAccessor,
+  CheckboxControlValueAccessor, SelectControlValueAccessor, SelectMultipleControlValueAccessor,
+  RadioControlValueAccessor, NgControlStatus, RequiredValidator, MinLengthValidator,
+  MaxLengthValidator, PatternValidator
+];
 
+const TEMPLATE_DRIVEN_DIRECTIVES: Type[] = /*@ts2dart_const*/[NgModel, NgModelGroup, NgForm];
+
+const REACTIVE_DRIVEN_DIRECTIVES: Type[] = /*@ts2dart_const*/[
+  FormControlDirective, FormGroupDirective, FormControlName, FormGroupName, FormArrayName
+];
 
 /**
  *
@@ -63,20 +74,12 @@ export {MaxLengthValidator, MinLengthValidator, PatternValidator, RequiredValida
  * ```
  * @experimental
  */
-export const FORM_DIRECTIVES: Type[] = /*@ts2dart_const*/[
-  NgModel, NgModelGroup, NgForm,
-
-  NgSelectOption, NgSelectMultipleOption, DefaultValueAccessor, NumberValueAccessor,
-  CheckboxControlValueAccessor, SelectControlValueAccessor, SelectMultipleControlValueAccessor,
-  RadioControlValueAccessor, NgControlStatus,
-
-  RequiredValidator, MinLengthValidator, MaxLengthValidator, PatternValidator
-];
+export const FORM_DIRECTIVES: Type[][] =
+    /*@ts2dart_const*/[TEMPLATE_DRIVEN_DIRECTIVES, SHARED_FORM_DIRECTIVES];
 
 /**
  * @experimental
  */
-export const REACTIVE_FORM_DIRECTIVES: Type[] =
-    /*@ts2dart_const*/[
-      FormControlDirective, FormGroupDirective, FormControlName, FormGroupName, FormArrayName
-    ];
+
+export const REACTIVE_FORM_DIRECTIVES: Type[][] =
+    /*@ts2dart_const*/[REACTIVE_DRIVEN_DIRECTIVES, SHARED_FORM_DIRECTIVES];