fix: small quality of life fixes for A11yMenu

- Removes the sliding animation that was visible when opening the menu
  UI to a page other than the first page.
- Dismisses the notification shade when opening the menu UI so that
  actions like SHOW_RECENTS can succeed when the service was triggered
  while notifications were open.

Test: observe animation is gone and notif shade is closed
Test: atest AccessibilityMenuServiceTest; observe existing tests pass
Fix: 419422134
Flag: EXEMPT low risk bugfix
Change-Id: I97e9d01779d37a16b22c011bf51444deb89b6db2