docs(common): update ngFor docs to new `as` syntax (#15166)

packages/common/src/directives/ng_for_of.ts

@@ -45,7 +45,7 @@ export class NgForOfContext<T> {
  * - `odd: boolean`: True when the item has an odd index in the iterable.
  *
  * ```
- * <li *ngFor="let user of userObservable | async as users; indexes as i; first as isFirst">
+ * <li *ngFor="let user of userObservable | async as users; index as i; first as isFirst">
  *    {{i}}/{{users.length}}. {{user}} <span *ngIf="isFirst">default</span>
  * </li>
  * ```
@@ -78,8 +78,8 @@ export class NgForOfContext<T> {
  *
  * ### Syntax
  *
- * - `<li *ngFor="let item of items; let i = index; trackBy: trackByFn">...</li>`
+ * - `<li *ngFor="let item of items; index as i; trackBy: trackByFn">...</li>`
- * - `<li template="ngFor let item of items; let i = index; trackBy: trackByFn">...</li>`
+ * - `<li template="ngFor let item of items; index as i; trackBy: trackByFn">...</li>`
  *
  * With `<ng-template>` element:
  *

packages/examples/forms/ts/nestedFormArray/nested_form_array_example.ts

@@ -16,7 +16,7 @@ import {FormArray, FormControl, FormGroup} from '@angular/forms';
   template: `
     <form [formGroup]="form" (ngSubmit)="onSubmit()">
       <div formArrayName="cities">
-        <div *ngFor="let city of cities.controls; let i=index">
+        <div *ngFor="let city of cities.controls; index as i">
           <input [formControlName]="i" placeholder="City">
         </div>
       </div>

packages/forms/src/directives/error_examples.ts

@@ -34,7 +34,7 @@ export const FormErrorExamples = {
   formArrayName: `
     <div [formGroup]="myGroup">
       <div formArrayName="cities">
-        <div *ngFor="let city of cityArray.controls; let i=index">
+        <div *ngFor="let city of cityArray.controls; index as i">
           <input [formControlName]="i">
         </div>
       </div>
@@ -61,4 +61,3 @@ export const FormErrorExamples = {
     </div>
   `
 };
-