Uses DisplayManager to get default display for landscape layout.

The previous mLayout.getDisplay() was returning null, causing this code
path to trigger a NPE in display.getRotation() for landscape devices.

Bug: 261252772
Test: Install AccessibilityMenu on a large-screen device.
      Enable the a11y service and interact with the UI.
Change-Id: Ie4f96ba22e9874c81d70b5ad449c3ead5da437ff