chore: reorganize cdk/a11y directory structure

* Since the `@angular/cdk/a11y` has grown a lot, it's becoming harder to navigate. These changes distribute the files into directories similarly to how we do it in `overlay`.
* Removes individual imports from the focus trap tests in favor of importing the `A11yModule`.

Author: crisbeto

src/cdk/a11y/a11y-module.ts

@@ -9,11 +9,15 @@
 import {PlatformModule} from '@angular/cdk/platform';
 import {CommonModule} from '@angular/common';
 import {NgModule} from '@angular/core';
-import {ARIA_DESCRIBER_PROVIDER, AriaDescriber} from './aria-describer';
-import {CdkMonitorFocus, FOCUS_MONITOR_PROVIDER} from './focus-monitor';
-import {CdkTrapFocus, FocusTrapDeprecatedDirective, FocusTrapFactory} from './focus-trap';
-import {InteractivityChecker} from './interactivity-checker';
-import {LIVE_ANNOUNCER_PROVIDER} from './live-announcer';
+import {ARIA_DESCRIBER_PROVIDER, AriaDescriber} from './aria-describer/aria-describer';
+import {CdkMonitorFocus, FOCUS_MONITOR_PROVIDER} from './focus-monitor/focus-monitor';
+import {
+  CdkTrapFocus,
+  FocusTrapDeprecatedDirective,
+  FocusTrapFactory,
+} from './focus-trap/focus-trap';
+import {InteractivityChecker} from './interactivity-checker/interactivity-checker';
+import {LIVE_ANNOUNCER_PROVIDER} from './live-announcer/live-announcer';
 
 @NgModule({
   imports: [CommonModule, PlatformModule],

src/cdk/a11y/aria-describer.spec.ts renamed to src/cdk/a11y/aria-describer/aria-describer.spec.ts

@@ -1,4 +1,4 @@
-import {A11yModule, CDK_DESCRIBEDBY_HOST_ATTRIBUTE} from './index';
+import {A11yModule, CDK_DESCRIBEDBY_HOST_ATTRIBUTE} from '../index';
 import {AriaDescriber, MESSAGES_CONTAINER_ID} from './aria-describer';
 import {async, ComponentFixture, TestBed} from '@angular/core/testing';
 import {Component, ElementRef, ViewChild} from '@angular/core';

src/cdk/a11y/aria-describer.ts renamed to src/cdk/a11y/aria-describer/aria-describer.ts

@@ -9,7 +9,7 @@ import {Component} from '@angular/core';
 import {ComponentFixture, fakeAsync, inject, TestBed, tick} from '@angular/core/testing';
 import {By} from '@angular/platform-browser';
 import {FocusMonitor, FocusOrigin, TOUCH_BUFFER_MS} from './focus-monitor';
-import {A11yModule} from './index';
+import {A11yModule} from '../index';
 
 
 describe('FocusMonitor', () => {

src/cdk/a11y/aria-reference.spec.ts renamed to src/cdk/a11y/aria-describer/aria-reference.spec.ts

@@ -1,24 +1,22 @@
 import {Platform} from '@angular/cdk/platform';
 import {Component, ViewChild} from '@angular/core';
 import {async, ComponentFixture, TestBed} from '@angular/core/testing';
-import {FocusTrap, CdkTrapFocus, FocusTrapFactory} from './focus-trap';
-import {InteractivityChecker} from './interactivity-checker';
+import {A11yModule, FocusTrap, CdkTrapFocus} from '../index';
 
 
 describe('FocusTrap', () => {
 
   beforeEach(async(() => {
     TestBed.configureTestingModule({
+      imports: [A11yModule],
       declarations: [
-        CdkTrapFocus,
         FocusTrapWithBindings,
         SimpleFocusTrap,
         FocusTrapTargets,
         FocusTrapWithSvg,
         FocusTrapWithoutFocusableElements,
         FocusTrapWithAutoCapture,
       ],
-      providers: [InteractivityChecker, Platform, FocusTrapFactory]
     });
 
     TestBed.compileComponents();

src/cdk/a11y/aria-reference.ts renamed to src/cdk/a11y/aria-describer/aria-reference.ts

@@ -18,7 +18,7 @@ import {
 } from '@angular/core';
 import {coerceBooleanProperty} from '@angular/cdk/coercion';
 import {take} from 'rxjs/operators/take';
-import {InteractivityChecker} from './interactivity-checker';
+import {InteractivityChecker} from '../interactivity-checker/interactivity-checker';
 import {DOCUMENT} from '@angular/common';
 
 

src/cdk/a11y/focus-monitor.spec.ts renamed to src/cdk/a11y/focus-monitor/focus-monitor.spec.ts

@@ -7,7 +7,7 @@
  */
 
 import {ListKeyManager, ListKeyManagerOption} from './list-key-manager';
-import {FocusOrigin} from './focus-monitor';
+import {FocusOrigin} from '../focus-monitor/focus-monitor';
 
 /**
  * This is the interface for focusable items (used by the FocusKeyManager).

src/cdk/a11y/focus-monitor.ts renamed to src/cdk/a11y/focus-monitor/focus-monitor.ts

@@ -2,11 +2,11 @@ import {DOWN_ARROW, TAB, UP_ARROW, LEFT_ARROW, RIGHT_ARROW} from '@angular/cdk/k
 import {take} from 'rxjs/operators/take';
 import {QueryList} from '@angular/core';
 import {fakeAsync, tick} from '@angular/core/testing';
-import {createKeyboardEvent} from '../testing/event-objects';
+import {createKeyboardEvent} from '@angular/cdk/testing';
 import {ActiveDescendantKeyManager} from './activedescendant-key-manager';
 import {FocusKeyManager} from './focus-key-manager';
 import {ListKeyManager} from './list-key-manager';
-import {FocusOrigin} from './focus-monitor';
+import {FocusOrigin} from '../focus-monitor/focus-monitor';
 import {Subject} from 'rxjs/Subject';
 
 

src/cdk/a11y/focus-trap.md renamed to src/cdk/a11y/focus-trap/focus-trap.md

@@ -2,7 +2,7 @@ import {inject, fakeAsync, tick, ComponentFixture, TestBed} from '@angular/core/
 import {Component} from '@angular/core';
 import {By} from '@angular/platform-browser';
 import {LiveAnnouncer, LIVE_ANNOUNCER_ELEMENT_TOKEN} from './live-announcer';
-import {A11yModule} from './index';
+import {A11yModule} from '../index';
 
 
 describe('LiveAnnouncer', () => {

src/cdk/a11y/focus-trap.spec.ts renamed to src/cdk/a11y/focus-trap/focus-trap.spec.ts

@@ -5,18 +5,18 @@
  * Use of this source code is governed by an MIT-style license that can be
  * found in the LICENSE file at https://angular.io/license
  */
-import {CdkTrapFocus} from './focus-trap';
+import {CdkTrapFocus} from './focus-trap/focus-trap';
 
 
-export * from './activedescendant-key-manager';
-export * from './aria-describer';
+export * from './aria-describer/aria-describer';
+export * from './key-manager/activedescendant-key-manager';
+export * from './key-manager/focus-key-manager';
+export * from './key-manager/list-key-manager';
+export * from './focus-trap/focus-trap';
+export * from './interactivity-checker/interactivity-checker';
+export * from './live-announcer/live-announcer';
+export * from './focus-monitor/focus-monitor';
 export * from './fake-mousedown';
-export * from './focus-key-manager';
-export * from './focus-trap';
-export * from './interactivity-checker';
-export * from './list-key-manager';
-export * from './live-announcer';
-export * from './focus-monitor';
 export * from './a11y-module';
 
 /**