Fix Toast leak in AccessibilityManager

 AccessibilityManager registers a client object in the constructor.
 So only create a AccessibilityManager when trying to send an accessibility event,
  as there may be multiple ToastPresenters initialized without being used: from the client app and SystemUi.

Test: atest WindowUntrustedTouchTest
 atest ToastWindowTest
 atest ToastPresenterTest
 atest ToastUITest

Bug: 298593662
Change-Id: Ie8a4440338d25d521eb036dc4531c820d5a35267