fix(stepper): support going to first/last steps via home/end keys (#9632)

Adds support for the user to skip to the first/last step in the stepper using the home and end keys. [Based on the a11y guidelines](https://www.w3.org/TR/wai-aria-practices-1.1/#tabpanel).

src/cdk/stepper/stepper.ts

@@ -27,7 +27,16 @@ import {
   OnChanges,
   OnDestroy
 } from '@angular/core';
-import {LEFT_ARROW, RIGHT_ARROW, DOWN_ARROW, UP_ARROW, ENTER, SPACE} from '@angular/cdk/keycodes';
+import {
+  LEFT_ARROW,
+  RIGHT_ARROW,
+  DOWN_ARROW,
+  UP_ARROW,
+  ENTER,
+  SPACE,
+  HOME,
+  END,
+} from '@angular/cdk/keycodes';
 import {CdkStepLabel} from './step-label';
 import {coerceBooleanProperty} from '@angular/cdk/coercion';
 import {AbstractControl} from '@angular/forms';
@@ -307,6 +316,16 @@ export class CdkStepper implements OnDestroy {
       this.selectedIndex = this._focusIndex;
       event.preventDefault();
     }
+
+    if (keyCode === HOME) {
+      this._focusStep(0);
+      event.preventDefault();
+    }
+
+    if (keyCode === END) {
+      this._focusStep(this._steps.length - 1);
+      event.preventDefault();
+    }
   }
 
   private _focusNextStep() {

src/lib/stepper/stepper.spec.ts

@@ -1,5 +1,14 @@
 import {Directionality} from '@angular/cdk/bidi';
-import {ENTER, LEFT_ARROW, RIGHT_ARROW, UP_ARROW, DOWN_ARROW, SPACE} from '@angular/cdk/keycodes';
+import {
+  ENTER,
+  LEFT_ARROW,
+  RIGHT_ARROW,
+  UP_ARROW,
+  DOWN_ARROW,
+  SPACE,
+  HOME,
+  END,
+} from '@angular/cdk/keycodes';
 import {dispatchKeyboardEvent} from '@angular/cdk/testing';
 import {Component, DebugElement} from '@angular/core';
 import {async, ComponentFixture, TestBed, inject} from '@angular/core/testing';
@@ -725,6 +734,16 @@ function assertCorrectKeyboardInteraction(fixture: ComponentFixture<any>,
   expect(stepperComponent.selectedIndex)
       .toBe(0,
           'Expected index of selected step to change to index of focused step after SPACE event.');
+
+  const endEvent = dispatchKeyboardEvent(stepHeaderEl, 'keydown', END);
+  expect(stepperComponent._focusIndex)
+      .toBe(stepHeaders.length - 1, 'Expected last step to be focused when pressing END.');
+  expect(endEvent.defaultPrevented).toBe(true, 'Expected default END action to be prevented.');
+
+  const homeEvent = dispatchKeyboardEvent(stepHeaderEl, 'keydown', HOME);
+  expect(stepperComponent._focusIndex)
+      .toBe(0, 'Expected first step to be focused when pressing HOME.');
+  expect(homeEvent.defaultPrevented).toBe(true, 'Expected default HOME action to be prevented.');
 }
 
 /** Asserts that step selection change using stepper buttons does not focus step header. */