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
```

tools/public_api_guard/common/index.d.ts

@@ -162,6 +162,10 @@ export declare class DefaultValueAccessor implements ControlValueAccessor {
     writeValue(value: any): void;
 }
 
+/** @deprecated */
+export declare class DeprecatedFormsModule {
+}
+
 /** @experimental */
 export interface Form {
     addControl(dir: NgControl): void;

tools/public_api_guard/forms/index.d.ts

@@ -101,9 +101,6 @@ export declare class DefaultValueAccessor implements ControlValueAccessor {
     writeValue(value: any): void;
 }
 
-/** @experimental */
-export declare function disableDeprecatedForms(): any[];
-
 /** @experimental */
 export interface Form {
     addControl(dir: NgControl): void;
@@ -116,7 +113,7 @@ export interface Form {
 }
 
 /** @experimental */
-export declare const FORM_DIRECTIVES: Type[];
+export declare const FORM_DIRECTIVES: Type[][];
 
 /** @experimental */
 export declare const FORM_PROVIDERS: Type[];
@@ -246,6 +243,10 @@ export declare class FormGroupName extends AbstractFormGroupDirective implements
     constructor(parent: ControlContainer, validators: any[], asyncValidators: any[]);
 }
 
+/** @experimental */
+export declare class FormsModule {
+}
+
 /** @experimental */
 export declare class MaxLengthValidator implements Validator {
     constructor(maxLength: string);
@@ -358,10 +359,14 @@ export declare class PatternValidator implements Validator {
 }
 
 /** @experimental */
-export declare function provideForms(): any[];
+export declare const REACTIVE_FORM_DIRECTIVES: Type[][];
 
 /** @experimental */
-export declare const REACTIVE_FORM_DIRECTIVES: Type[];
+export declare const REACTIVE_FORM_PROVIDERS: Type[];
+
+/** @experimental */
+export declare class ReactiveFormsModule {
+}
 
 /** @experimental */
 export declare class RequiredValidator {