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

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

@@ -0,0 +1,54 @@
+
+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';
+
+
+
+/*
+ * 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 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 function provideForms(): any[] {
+  return [
+    {provide: PLATFORM_DIRECTIVES, useValue: NEW_FORM_DIRECTIVES, multi: true}, FORM_PROVIDERS
+  ];
+}