chore: reorganize cdk/a11y directory structure (#9389)

* 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';